Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $157.84   11.526%   $176.0326   $176.03   $176.05   $176.00  
  Purchase #2 $194.39   7.372%   $208.7204   $208.72   $208.70   $208.70  
  Purchase #3 $170.88   6.342%   $181.7172   $181.72   $181.70   $181.70  
  Purchase #4 $241.67   6.711%   $257.8885   $257.89   $257.90   $257.90  
  Purchase #5 $163.46   6.656%   $174.3399   $174.34   $174.35   $174.30  
  Purchase #6 $143.95   11.386%   $160.3401   $160.34   $160.35   $160.30  
  Purchase #7 $211.79   5.605%   $223.6608   $223.66   $223.65   $223.70  
  7 purchase totals = $1,283.98       $1,382.6995   $1,382.70   $1,382.70   $1,382.60