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 $183.44   7.802%   $197.752   $197.75   $197.75   $197.80  
  Purchase #2 $64.67   3.667%   $67.0414   $67.04   $67.05   $67.00  
  Purchase #3 $28.82   5.395%   $30.3748   $30.37   $30.35   $30.40  
  Purchase #4 $184.93   9.351%   $202.2228   $202.22   $202.20   $202.20  
  Purchase #5 $153.52   13.718%   $174.5799   $174.58   $174.60   $174.60  
  Purchase #6 $153.45   5.244%   $161.4969   $161.50   $161.50   $161.50  
  Purchase #7 $110.99   7.126%   $118.8991   $118.90   $118.90   $118.90  
  7 purchase totals = $879.82       $952.3669   $952.36   $952.35   $952.40