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 $95.98   8.761%   $104.3888   $104.39   $104.40   $104.40  
  Purchase #2 $236.59   13.795%   $269.2276   $269.23   $269.25   $269.20  
  Purchase #3 $79.25   7.281%   $85.0202   $85.02   $85.00   $85.00  
  Purchase #4 $78.49   8.362%   $85.0533   $85.05   $85.05   $85.10  
  Purchase #5 $150.68   11.685%   $168.287   $168.29   $168.30   $168.30  
  Purchase #6 $188.74   6.873%   $201.7121   $201.71   $201.70   $201.70  
  Purchase #7 $129.35   11.268%   $143.9252   $143.93   $143.95   $143.90  
  7 purchase totals = $959.08       $1,057.6142   $1,057.62   $1,057.65   $1,057.60