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 $90.34   5.165%   $95.0061   $95.01   $95.00   $95.00  
  Purchase #2 $229.41   10.454%   $253.3925   $253.39   $253.40   $253.40  
  Purchase #3 $205.31   13.353%   $232.725   $232.73   $232.75   $232.70  
  Purchase #4 $161.29   12.458%   $181.3835   $181.38   $181.40   $181.40  
  Purchase #5 $96.25   6.112%   $102.1328   $102.13   $102.15   $102.10  
  Purchase #6 $25.33   9.388%   $27.708   $27.71   $27.70   $27.70  
  Purchase #7 $111.97   7.122%   $119.9445   $119.94   $119.95   $119.90  
  7 purchase totals = $919.90       $1,012.2924   $1,012.29   $1,012.35   $1,012.20