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 $75.99   8.154%   $82.1862   $82.19   $82.20   $82.20  
  Purchase #2 $194.91   6.145%   $206.8872   $206.89   $206.90   $206.90  
  Purchase #3 $155.81   5.651%   $164.6148   $164.61   $164.60   $164.60  
  Purchase #4 $52.53   10.421%   $58.0042   $58.00   $58.00   $58.00  
  Purchase #5 $71.79   12.771%   $80.9583   $80.96   $80.95   $81.00  
  Purchase #6 $52.67   10.675%   $58.2925   $58.29   $58.30   $58.30  
  Purchase #7 $111.65   6.637%   $119.0602   $119.06   $119.05   $119.10  
  7 purchase totals = $715.35       $770.0034   $770.00   $770.00   $770.10