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 $176.49   13.163%   $199.7214   $199.72   $199.70   $199.70  
  Purchase #2 $85.46   13.216%   $96.7544   $96.75   $96.75   $96.80  
  Purchase #3 $201.48   8.160%   $217.9208   $217.92   $217.90   $217.90  
  Purchase #4 $199.34   5.862%   $211.0253   $211.03   $211.05   $211.00  
  Purchase #5 $205.44   8.801%   $223.5208   $223.52   $223.50   $223.50  
  Purchase #6 $247.57   4.773%   $259.3865   $259.39   $259.40   $259.40  
  Purchase #7 $247.37   12.124%   $277.3611   $277.36   $277.35   $277.40  
  7 purchase totals = $1,363.15       $1,485.6903   $1,485.69   $1,485.65   $1,485.70