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 $161.42   12.867%   $182.1899   $182.19   $182.20   $182.20  
  Purchase #2 $236.55   13.662%   $268.8675   $268.87   $268.85   $268.90  
  Purchase #3 $112.97   6.864%   $120.7243   $120.72   $120.70   $120.70  
  Purchase #4 $163.71   6.495%   $174.343   $174.34   $174.35   $174.30  
  Purchase #5 $137.30   5.826%   $145.2991   $145.30   $145.30   $145.30  
  Purchase #6 $25.58   7.239%   $27.4317   $27.43   $27.45   $27.40  
  Purchase #7 $197.39   7.750%   $212.6877   $212.69   $212.70   $212.70  
  7 purchase totals = $1,034.92       $1,131.5432   $1,131.54   $1,131.55   $1,131.50