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 $60.38   9.237%   $65.9573   $65.96   $65.95   $66.00  
  Purchase #2 $233.97   9.705%   $256.6768   $256.68   $256.70   $256.70  
  Purchase #3 $36.27   5.244%   $38.172   $38.17   $38.15   $38.20  
  Purchase #4 $233.34   10.474%   $257.78   $257.78   $257.80   $257.80  
  Purchase #5 $246.65   11.109%   $274.0503   $274.05   $274.05   $274.10  
  Purchase #6 $39.31   6.704%   $41.9453   $41.95   $41.95   $41.90  
  Purchase #7 $186.43   13.644%   $211.8665   $211.87   $211.85   $211.90  
  7 purchase totals = $1,036.35       $1,146.4482   $1,146.46   $1,146.45   $1,146.60