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 $149.52   11.433%   $166.6146   $166.61   $166.60   $166.60  
  Purchase #2 $88.41   7.392%   $94.9453   $94.95   $94.95   $94.90  
  Purchase #3 $166.77   4.647%   $174.5198   $174.52   $174.50   $174.50  
  Purchase #4 $64.79   6.111%   $68.7493   $68.75   $68.75   $68.70  
  Purchase #5 $160.63   8.303%   $173.9671   $173.97   $173.95   $174.00  
  Purchase #6 $250.40   10.158%   $275.8356   $275.84   $275.85   $275.80  
  Purchase #7 $13.42   9.538%   $14.7   $14.70   $14.70   $14.70  
  7 purchase totals = $893.94       $969.3317   $969.34   $969.30   $969.20