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 $249.46   10.475%   $275.5909   $275.59   $275.60   $275.60  
  Purchase #2 $212.52   9.406%   $232.5096   $232.51   $232.50   $232.50  
  Purchase #3 $126.35   7.851%   $136.2697   $136.27   $136.25   $136.30  
  Purchase #4 $209.79   4.707%   $219.6648   $219.66   $219.65   $219.70  
  Purchase #5 $16.86   5.309%   $17.7551   $17.76   $17.75   $17.80  
  Purchase #6 $247.74   3.427%   $256.23   $256.23   $256.25   $256.20  
  Purchase #7 $31.78   10.267%   $35.0429   $35.04   $35.05   $35.00  
  7 purchase totals = $1,094.50       $1,173.0630   $1,173.06   $1,173.05   $1,173.10