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 $61.86   13.117%   $69.9742   $69.97   $69.95   $70.00  
  Purchase #2 $102.53   9.344%   $112.1104   $112.11   $112.10   $112.10  
  Purchase #3 $56.39   13.523%   $64.0156   $64.02   $64.00   $64.00  
  Purchase #4 $235.56   3.342%   $243.4324   $243.43   $243.45   $243.40  
  Purchase #5 $209.42   9.795%   $229.9327   $229.93   $229.95   $229.90  
  Purchase #6 $95.27   10.869%   $105.6249   $105.62   $105.60   $105.60  
  Purchase #7 $204.66   13.482%   $232.2523   $232.25   $232.25   $232.30  
  7 purchase totals = $965.69       $1,057.3425   $1,057.33   $1,057.30   $1,057.30