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 $182.96   9.803%   $200.8956   $200.90   $200.90   $200.90  
  Purchase #2 $138.96   8.631%   $150.9536   $150.95   $150.95   $151.00  
  Purchase #3 $183.65   11.349%   $204.4924   $204.49   $204.50   $204.50  
  Purchase #4 $243.77   4.521%   $254.7908   $254.79   $254.80   $254.80  
  Purchase #5 $58.35   10.489%   $64.4703   $64.47   $64.45   $64.50  
  Purchase #6 $140.63   9.749%   $154.34   $154.34   $154.35   $154.30  
  Purchase #7 $229.33   5.410%   $241.7368   $241.74   $241.75   $241.70  
  7 purchase totals = $1,177.65       $1,271.6795   $1,271.68   $1,271.70   $1,271.70