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 $118.39   5.572%   $124.9867   $124.99   $125.00   $125.00  
  Purchase #2 $242.73   8.444%   $263.2261   $263.23   $263.25   $263.20  
  Purchase #3 $78.68   7.672%   $84.7163   $84.72   $84.70   $84.70  
  Purchase #4 $157.52   12.404%   $177.0588   $177.06   $177.05   $177.10  
  Purchase #5 $204.85   9.682%   $224.6836   $224.68   $224.70   $224.70  
  Purchase #6 $169.75   6.472%   $180.7362   $180.74   $180.75   $180.70  
  Purchase #7 $210.68   12.249%   $236.4862   $236.49   $236.50   $236.50  
  7 purchase totals = $1,182.60       $1,291.8939   $1,291.91   $1,291.95   $1,291.90