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 $54.33   11.222%   $60.4269   $60.43   $60.45   $60.40  
  Purchase #2 $214.78   10.870%   $238.1266   $238.13   $238.15   $238.10  
  Purchase #3 $220.86   4.615%   $231.0527   $231.05   $231.05   $231.10  
  Purchase #4 $46.57   9.332%   $50.9159   $50.92   $50.90   $50.90  
  Purchase #5 $23.50   11.216%   $26.1358   $26.14   $26.15   $26.10  
  Purchase #6 $206.55   3.134%   $213.0233   $213.02   $213.00   $213.00  
  Purchase #7 $99.25   4.104%   $103.3232   $103.32   $103.30   $103.30  
  7 purchase totals = $865.84       $923.0044   $923.01   $923.00   $922.90