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 $209.47   4.141%   $218.1442   $218.14   $218.15   $218.10  
  Purchase #2 $130.95   6.462%   $139.412   $139.41   $139.40   $139.40  
  Purchase #3 $229.90   6.741%   $245.3976   $245.40   $245.40   $245.40  
  Purchase #4 $20.52   10.608%   $22.6968   $22.70   $22.70   $22.70  
  Purchase #5 $87.41   4.166%   $91.0515   $91.05   $91.05   $91.10  
  Purchase #6 $80.51   6.254%   $85.5451   $85.55   $85.55   $85.50  
  Purchase #7 $42.74   13.850%   $48.6595   $48.66   $48.65   $48.70  
  7 purchase totals = $801.50       $850.9067   $850.91   $850.90   $850.90