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 $56.94   10.484%   $62.9096   $62.91   $62.90   $62.90  
  Purchase #2 $204.74   7.452%   $219.9972   $220.00   $220.00   $220.00  
  Purchase #3 $153.86   6.163%   $163.3424   $163.34   $163.35   $163.30  
  Purchase #4 $95.79   4.273%   $99.8831   $99.88   $99.90   $99.90  
  Purchase #5 $42.53   4.719%   $44.537   $44.54   $44.55   $44.50  
  Purchase #6 $235.61   10.239%   $259.7341   $259.73   $259.75   $259.70  
  Purchase #7 $155.97   9.275%   $170.4362   $170.44   $170.45   $170.40  
  7 purchase totals = $945.44       $1,020.8396   $1,020.84   $1,020.90   $1,020.70