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 $136.37   10.638%   $150.877   $150.88   $150.90   $150.90  
  Purchase #2 $109.89   7.235%   $117.8405   $117.84   $117.85   $117.80  
  Purchase #3 $141.87   7.571%   $152.611   $152.61   $152.60   $152.60  
  Purchase #4 $207.54   5.763%   $219.5005   $219.50   $219.50   $219.50  
  Purchase #5 $83.93   11.620%   $93.6827   $93.68   $93.70   $93.70  
  Purchase #6 $83.65   6.362%   $88.9718   $88.97   $88.95   $89.00  
  Purchase #7 $204.84   13.512%   $232.518   $232.52   $232.50   $232.50  
  7 purchase totals = $968.09       $1,056.0015   $1,056.00   $1,056.00   $1,056.00