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 $242.35   11.830%   $271.02   $271.02   $271.00   $271.00  
  Purchase #2 $31.39   11.327%   $34.9455   $34.95   $34.95   $34.90  
  Purchase #3 $109.71   6.483%   $116.8225   $116.82   $116.80   $116.80  
  Purchase #4 $197.59   7.694%   $212.7926   $212.79   $212.80   $212.80  
  Purchase #5 $53.79   7.618%   $57.8877   $57.89   $57.90   $57.90  
  Purchase #6 $229.36   10.236%   $252.8373   $252.84   $252.85   $252.80  
  Purchase #7 $243.49   7.468%   $261.6738   $261.67   $261.65   $261.70  
  7 purchase totals = $1,107.68       $1,207.9794   $1,207.98   $1,207.95   $1,207.90