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 $57.98   8.707%   $63.0283   $63.03   $63.05   $63.00  
  Purchase #2 $150.78   12.489%   $169.6109   $169.61   $169.60   $169.60  
  Purchase #3 $173.89   13.335%   $197.0782   $197.08   $197.10   $197.10  
  Purchase #4 $38.69   5.336%   $40.7545   $40.75   $40.75   $40.80  
  Purchase #5 $248.26   13.801%   $282.5224   $282.52   $282.50   $282.50  
  Purchase #6 $48.74   12.334%   $54.7516   $54.75   $54.75   $54.80  
  Purchase #7 $246.96   11.287%   $274.8344   $274.83   $274.85   $274.80  
  7 purchase totals = $965.30       $1,082.5803   $1,082.57   $1,082.60   $1,082.60