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 $82.44   6.687%   $87.9528   $87.95   $87.95   $88.00  
  Purchase #2 $37.48   10.536%   $41.4289   $41.43   $41.45   $41.40  
  Purchase #3 $236.40   13.331%   $267.9145   $267.91   $267.90   $267.90  
  Purchase #4 $50.56   12.598%   $56.9295   $56.93   $56.95   $56.90  
  Purchase #5 $82.35   12.431%   $92.5869   $92.59   $92.60   $92.60  
  Purchase #6 $174.80   6.759%   $186.6147   $186.61   $186.60   $186.60  
  Purchase #7 $57.77   13.444%   $65.5366   $65.54   $65.55   $65.50  
  7 purchase totals = $721.80       $798.9639   $798.96   $799.00   $798.90