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 $204.95   3.641%   $212.4122   $212.41   $212.40   $212.40  
  Purchase #2 $94.85   10.310%   $104.629   $104.63   $104.65   $104.60  
  Purchase #3 $109.81   10.255%   $121.071   $121.07   $121.05   $121.10  
  Purchase #4 $56.52   8.504%   $61.3265   $61.33   $61.35   $61.30  
  Purchase #5 $215.92   9.788%   $237.0542   $237.05   $237.05   $237.10  
  Purchase #6 $138.98   8.293%   $150.5056   $150.51   $150.50   $150.50  
  Purchase #7 $65.50   3.800%   $67.989   $67.99   $68.00   $68.00  
  7 purchase totals = $886.53       $954.9875   $954.99   $955.00   $955.00