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 $118.62   13.431%   $134.5519   $134.55   $134.55   $134.60  
  Purchase #2 $200.65   11.131%   $222.9844   $222.98   $223.00   $223.00  
  Purchase #3 $97.36   11.295%   $108.3568   $108.36   $108.35   $108.40  
  Purchase #4 $36.84   9.870%   $40.4761   $40.48   $40.50   $40.50  
  Purchase #5 $122.90   3.773%   $127.537   $127.54   $127.55   $127.50  
  Purchase #6 $118.89   6.342%   $126.43   $126.43   $126.45   $126.40  
  Purchase #7 $68.64   9.363%   $75.0668   $75.07   $75.05   $75.10  
  7 purchase totals = $763.90       $835.4030   $835.41   $835.45   $835.50