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 $73.39   3.404%   $75.8882   $75.89   $75.90   $75.90  
  Purchase #2 $194.33   6.808%   $207.56   $207.56   $207.55   $207.60  
  Purchase #3 $145.43   7.375%   $156.1555   $156.16   $156.15   $156.20  
  Purchase #4 $221.76   10.789%   $245.6857   $245.69   $245.70   $245.70  
  Purchase #5 $147.54   12.339%   $165.745   $165.75   $165.75   $165.70  
  Purchase #6 $197.40   9.650%   $216.4491   $216.45   $216.45   $216.40  
  Purchase #7 $104.33   11.190%   $116.0045   $116.00   $116.00   $116.00  
  7 purchase totals = $1,084.18       $1,183.4880   $1,183.50   $1,183.50   $1,183.50