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 $53.39   12.625%   $60.1305   $60.13   $60.15   $60.10  
  Purchase #2 $229.39   12.117%   $257.1852   $257.19   $257.20   $257.20  
  Purchase #3 $40.84   6.254%   $43.3941   $43.39   $43.40   $43.40  
  Purchase #4 $150.36   6.568%   $160.2356   $160.24   $160.25   $160.20  
  Purchase #5 $165.79   9.358%   $181.3046   $181.30   $181.30   $181.30  
  Purchase #6 $247.63   11.112%   $275.1466   $275.15   $275.15   $275.10  
  Purchase #7 $64.54   9.146%   $70.4428   $70.44   $70.45   $70.40  
  7 purchase totals = $951.94       $1,047.8394   $1,047.84   $1,047.90   $1,047.70