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 $82.65   13.789%   $94.0466   $94.05   $94.05   $94.00  
  Purchase #2 $43.37   10.599%   $47.9668   $47.97   $47.95   $48.00  
  Purchase #3 $164.30   7.179%   $176.0951   $176.10   $176.10   $176.10  
  Purchase #4 $243.31   9.816%   $267.1933   $267.19   $267.20   $267.20  
  Purchase #5 $97.55   3.461%   $100.9262   $100.93   $100.95   $100.90  
  Purchase #6 $86.31   5.349%   $90.9267   $90.93   $90.95   $90.90  
  Purchase #7 $55.57   9.364%   $60.7736   $60.77   $60.75   $60.80  
  7 purchase totals = $773.06       $837.9283   $837.94   $837.95   $837.90