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 $61.89   4.450%   $64.6441   $64.64   $64.65   $64.60  
  Purchase #2 $154.52   13.515%   $175.4034   $175.40   $175.40   $175.40  
  Purchase #3 $32.35   8.450%   $35.0836   $35.08   $35.10   $35.10  
  Purchase #4 $241.35   8.330%   $261.4545   $261.45   $261.45   $261.50  
  Purchase #5 $195.47   12.195%   $219.3076   $219.31   $219.30   $219.30  
  Purchase #6 $182.92   11.279%   $203.5515   $203.55   $203.55   $203.60  
  Purchase #7 $199.76   11.543%   $222.8183   $222.82   $222.80   $222.80  
  7 purchase totals = $1,068.26       $1,182.2630   $1,182.25   $1,182.25   $1,182.30