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 $58.77   10.745%   $65.0848   $65.08   $65.10   $65.10  
  Purchase #2 $98.55   5.741%   $104.2078   $104.21   $104.20   $104.20  
  Purchase #3 $26.44   10.479%   $29.2106   $29.21   $29.20   $29.20  
  Purchase #4 $49.72   10.701%   $55.0405   $55.04   $55.05   $55.00  
  Purchase #5 $167.58   8.683%   $182.131   $182.13   $182.15   $182.10  
  Purchase #6 $27.51   10.229%   $30.324   $30.32   $30.30   $30.30  
  Purchase #7 $12.95   6.597%   $13.8043   $13.80   $13.80   $13.80  
  7 purchase totals = $441.52       $479.8030   $479.79   $479.80   $479.70