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 $63.44   6.801%   $67.7546   $67.75   $67.75   $67.80  
  Purchase #2 $191.93   9.416%   $210.0021   $210.00   $210.00   $210.00  
  Purchase #3 $238.47   7.257%   $255.7758   $255.78   $255.80   $255.80  
  Purchase #4 $192.71   12.840%   $217.454   $217.45   $217.45   $217.50  
  Purchase #5 $129.54   4.604%   $135.504   $135.50   $135.50   $135.50  
  Purchase #6 $105.58   4.207%   $110.0218   $110.02   $110.00   $110.00  
  Purchase #7 $98.96   7.134%   $106.0198   $106.02   $106.00   $106.00  
  7 purchase totals = $1,020.63       $1,102.5321   $1,102.52   $1,102.50   $1,102.60