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 $154.42   9.422%   $168.9695   $168.97   $168.95   $169.00  
  Purchase #2 $65.98   3.612%   $68.3632   $68.36   $68.35   $68.40  
  Purchase #3 $173.78   4.148%   $180.9884   $180.99   $181.00   $181.00  
  Purchase #4 $27.62   6.861%   $29.515   $29.52   $29.50   $29.50  
  Purchase #5 $54.52   4.772%   $57.1217   $57.12   $57.10   $57.10  
  Purchase #6 $60.45   5.182%   $63.5825   $63.58   $63.60   $63.60  
  Purchase #7 $247.44   11.287%   $275.3686   $275.37   $275.35   $275.40  
  7 purchase totals = $784.21       $843.9089   $843.91   $843.85   $844.00