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 $116.86   13.196%   $132.2808   $132.28   $132.30   $132.30  
  Purchase #2 $156.95   4.279%   $163.6659   $163.67   $163.65   $163.70  
  Purchase #3 $43.49   4.853%   $45.6006   $45.60   $45.60   $45.60  
  Purchase #4 $81.26   9.342%   $88.8513   $88.85   $88.85   $88.90  
  Purchase #5 $152.78   4.388%   $159.484   $159.48   $159.50   $159.50  
  Purchase #6 $201.59   4.859%   $211.3853   $211.39   $211.40   $211.40  
  Purchase #7 $206.97   5.198%   $217.7283   $217.73   $217.75   $217.70  
  7 purchase totals = $959.90       $1,018.9962   $1,019.00   $1,019.05   $1,019.10