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 $196.57   6.491%   $209.3294   $209.33   $209.35   $209.30  
  Purchase #2 $200.28   8.655%   $217.6142   $217.61   $217.60   $217.60  
  Purchase #3 $66.96   13.252%   $75.8335   $75.83   $75.85   $75.80  
  Purchase #4 $105.39   9.364%   $115.2587   $115.26   $115.25   $115.30  
  Purchase #5 $98.51   7.647%   $106.0431   $106.04   $106.05   $106.00  
  Purchase #6 $207.45   8.338%   $224.7472   $224.75   $224.75   $224.70  
  Purchase #7 $66.46   12.454%   $74.7369   $74.74   $74.75   $74.70  
  7 purchase totals = $941.62       $1,023.5630   $1,023.56   $1,023.60   $1,023.40