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 $57.64   6.119%   $61.167   $61.17   $61.15   $61.20  
  Purchase #2 $206.61   8.511%   $224.1946   $224.19   $224.20   $224.20  
  Purchase #3 $19.29   11.128%   $21.4366   $21.44   $21.45   $21.40  
  Purchase #4 $48.30   5.653%   $51.0304   $51.03   $51.05   $51.00  
  Purchase #5 $120.52   11.442%   $134.3099   $134.31   $134.30   $134.30  
  Purchase #6 $223.73   5.244%   $235.4624   $235.46   $235.45   $235.50  
  Purchase #7 $183.31   6.581%   $195.3736   $195.37   $195.35   $195.40  
  7 purchase totals = $859.40       $922.9745   $922.97   $922.95   $923.00