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 $28.50   7.397%   $30.6081   $30.61   $30.60   $30.60  
  Purchase #2 $34.77   6.650%   $37.0822   $37.08   $37.10   $37.10  
  Purchase #3 $103.55   3.528%   $107.2032   $107.20   $107.20   $107.20  
  Purchase #4 $128.43   11.558%   $143.2739   $143.27   $143.25   $143.30  
  Purchase #5 $19.91   6.463%   $21.1968   $21.20   $21.20   $21.20  
  Purchase #6 $121.52   11.453%   $135.4377   $135.44   $135.45   $135.40  
  Purchase #7 $55.46   7.594%   $59.6716   $59.67   $59.65   $59.70  
  7 purchase totals = $492.14       $534.4735   $534.47   $534.45   $534.50