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 $118.66   12.124%   $133.0463   $133.05   $133.05   $133.00  
  Purchase #2 $24.66   13.340%   $27.9496   $27.95   $27.95   $27.90  
  Purchase #3 $229.89   7.614%   $247.3938   $247.39   $247.40   $247.40  
  Purchase #4 $192.81   6.170%   $204.7064   $204.71   $204.70   $204.70  
  Purchase #5 $197.36   3.465%   $204.1985   $204.20   $204.20   $204.20  
  Purchase #6 $56.30   5.198%   $59.2265   $59.23   $59.25   $59.20  
  Purchase #7 $147.30   6.360%   $156.6683   $156.67   $156.65   $156.70  
  7 purchase totals = $966.98       $1,033.1894   $1,033.20   $1,033.20   $1,033.10