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 $81.53   7.526%   $87.6659   $87.67   $87.65   $87.70  
  Purchase #2 $101.42   9.171%   $110.7212   $110.72   $110.70   $110.70  
  Purchase #3 $54.29   3.159%   $56.005   $56.01   $56.00   $56.00  
  Purchase #4 $243.71   13.558%   $276.7522   $276.75   $276.75   $276.80  
  Purchase #5 $133.38   5.528%   $140.7532   $140.75   $140.75   $140.80  
  Purchase #6 $244.45   8.821%   $266.0129   $266.01   $266.00   $266.00  
  Purchase #7 $61.67   6.287%   $65.5472   $65.55   $65.55   $65.50  
  7 purchase totals = $920.45       $1,003.4576   $1,003.46   $1,003.40   $1,003.50