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 $184.87   10.868%   $204.9617   $204.96   $204.95   $205.00  
  Purchase #2 $236.39   7.326%   $253.7079   $253.71   $253.70   $253.70  
  Purchase #3 $43.46   12.290%   $48.8012   $48.80   $48.80   $48.80  
  Purchase #4 $169.86   3.430%   $175.6862   $175.69   $175.70   $175.70  
  Purchase #5 $136.41   11.751%   $152.4395   $152.44   $152.45   $152.40  
  Purchase #6 $77.83   5.357%   $81.9994   $82.00   $82.00   $82.00  
  Purchase #7 $138.91   8.467%   $150.6715   $150.67   $150.65   $150.70  
  7 purchase totals = $987.73       $1,068.2674   $1,068.27   $1,068.25   $1,068.30