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 $37.25   12.582%   $41.9368   $41.94   $41.95   $41.90  
  Purchase #2 $58.79   10.295%   $64.8424   $64.84   $64.85   $64.80  
  Purchase #3 $41.67   4.425%   $43.5139   $43.51   $43.50   $43.50  
  Purchase #4 $97.76   8.115%   $105.6932   $105.69   $105.70   $105.70  
  Purchase #5 $229.30   8.460%   $248.6988   $248.70   $248.70   $248.70  
  Purchase #6 $225.96   7.352%   $242.5726   $242.57   $242.55   $242.60  
  Purchase #7 $229.68   10.740%   $254.3476   $254.35   $254.35   $254.30  
  7 purchase totals = $920.41       $1,001.6053   $1,001.60   $1,001.60   $1,001.50