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 $70.31   6.725%   $75.0383   $75.04   $75.05   $75.00  
  Purchase #2 $237.96   11.512%   $265.354   $265.35   $265.35   $265.40  
  Purchase #3 $93.81   5.801%   $99.2519   $99.25   $99.25   $99.30  
  Purchase #4 $206.35   6.676%   $220.1259   $220.13   $220.15   $220.10  
  Purchase #5 $120.95   11.455%   $134.8048   $134.80   $134.80   $134.80  
  Purchase #6 $123.89   9.762%   $135.9841   $135.98   $136.00   $136.00  
  Purchase #7 $139.35   8.858%   $151.6936   $151.69   $151.70   $151.70  
  7 purchase totals = $992.62       $1,082.2526   $1,082.24   $1,082.30   $1,082.30