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 $64.66   10.869%   $71.6879   $71.69   $71.70   $71.70  
  Purchase #2 $132.59   13.830%   $150.9272   $150.93   $150.95   $150.90  
  Purchase #3 $221.79   13.612%   $251.9801   $251.98   $252.00   $252.00  
  Purchase #4 $68.86   3.520%   $71.2839   $71.28   $71.30   $71.30  
  Purchase #5 $41.70   10.822%   $46.2128   $46.21   $46.20   $46.20  
  Purchase #6 $51.98   4.427%   $54.2812   $54.28   $54.30   $54.30  
  Purchase #7 $202.97   10.719%   $224.7264   $224.73   $224.75   $224.70  
  7 purchase totals = $784.55       $871.0995   $871.10   $871.20   $871.10