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 $174.57   11.194%   $194.1114   $194.11   $194.10   $194.10  
  Purchase #2 $142.32   7.382%   $152.8261   $152.83   $152.85   $152.80  
  Purchase #3 $20.94   11.464%   $23.3406   $23.34   $23.35   $23.30  
  Purchase #4 $228.28   9.426%   $249.7977   $249.80   $249.80   $249.80  
  Purchase #5 $119.80   10.362%   $132.2137   $132.21   $132.20   $132.20  
  Purchase #6 $154.46   7.852%   $166.5882   $166.59   $166.60   $166.60  
  Purchase #7 $218.47   10.178%   $240.7059   $240.71   $240.70   $240.70  
  7 purchase totals = $1,058.84       $1,159.5836   $1,159.59   $1,159.60   $1,159.50