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 $231.98   11.241%   $258.0569   $258.06   $258.05   $258.10  
  Purchase #2 $138.67   7.406%   $148.9399   $148.94   $148.95   $148.90  
  Purchase #3 $222.36   6.707%   $237.2737   $237.27   $237.25   $237.30  
  Purchase #4 $95.69   10.829%   $106.0523   $106.05   $106.05   $106.10  
  Purchase #5 $43.50   10.637%   $48.1271   $48.13   $48.15   $48.10  
  Purchase #6 $103.67   9.581%   $113.6026   $113.60   $113.60   $113.60  
  Purchase #7 $147.78   9.314%   $161.5442   $161.54   $161.55   $161.50  
  7 purchase totals = $983.65       $1,073.5967   $1,073.59   $1,073.60   $1,073.60