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 $202.33   10.194%   $222.9555   $222.96   $222.95   $223.00  
  Purchase #2 $117.40   7.448%   $126.144   $126.14   $126.15   $126.10  
  Purchase #3 $58.64   6.339%   $62.3572   $62.36   $62.35   $62.40  
  Purchase #4 $29.95   9.528%   $32.8036   $32.80   $32.80   $32.80  
  Purchase #5 $121.52   3.738%   $126.0624   $126.06   $126.05   $126.10  
  Purchase #6 $246.76   11.428%   $274.9597   $274.96   $274.95   $275.00  
  Purchase #7 $27.37   13.355%   $31.0253   $31.03   $31.05   $31.00  
  7 purchase totals = $803.97       $876.3077   $876.31   $876.30   $876.40