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 $59.30   4.816%   $62.1559   $62.16   $62.15   $62.20  
  Purchase #2 $227.67   10.151%   $250.7808   $250.78   $250.80   $250.80  
  Purchase #3 $22.85   13.848%   $26.0143   $26.01   $26.00   $26.00  
  Purchase #4 $45.80   13.551%   $52.0064   $52.01   $52.00   $52.00  
  Purchase #5 $23.61   8.595%   $25.6393   $25.64   $25.65   $25.60  
  Purchase #6 $15.87   8.858%   $17.2758   $17.28   $17.30   $17.30  
  Purchase #7 $148.62   11.263%   $165.3591   $165.36   $165.35   $165.40  
  7 purchase totals = $543.72       $599.2316   $599.24   $599.25   $599.30