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 $87.76   11.821%   $98.1341   $98.13   $98.15   $98.10  
  Purchase #2 $228.28   5.460%   $240.7441   $240.74   $240.75   $240.70  
  Purchase #3 $119.79   11.148%   $133.1442   $133.14   $133.15   $133.10  
  Purchase #4 $41.74   5.574%   $44.0666   $44.07   $44.05   $44.10  
  Purchase #5 $87.36   8.278%   $94.5917   $94.59   $94.60   $94.60  
  Purchase #6 $110.29   10.140%   $121.4734   $121.47   $121.45   $121.50  
  Purchase #7 $218.36   3.675%   $226.3847   $226.38   $226.40   $226.40  
  7 purchase totals = $893.58       $958.5388   $958.52   $958.55   $958.50