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 $52.66   11.127%   $58.5195   $58.52   $58.50   $58.50  
  Purchase #2 $130.50   6.792%   $139.3636   $139.36   $139.35   $139.40  
  Purchase #3 $217.64   5.508%   $229.6276   $229.63   $229.65   $229.60  
  Purchase #4 $95.92   4.789%   $100.5136   $100.51   $100.50   $100.50  
  Purchase #5 $5.73   9.702%   $6.2859   $6.29   $6.30   $6.30  
  Purchase #6 $211.95   6.629%   $226.0002   $226.00   $226.00   $226.00  
  Purchase #7 $154.80   3.774%   $160.6422   $160.64   $160.65   $160.60  
  7 purchase totals = $869.20       $920.9526   $920.95   $920.95   $920.90