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 $236.93   4.126%   $246.7057   $246.71   $246.70   $246.70  
  Purchase #2 $172.64   6.112%   $183.1918   $183.19   $183.20   $183.20  
  Purchase #3 $210.51   13.368%   $238.651   $238.65   $238.65   $238.70  
  Purchase #4 $60.60   3.202%   $62.5404   $62.54   $62.55   $62.50  
  Purchase #5 $225.68   6.800%   $241.0262   $241.03   $241.05   $241.00  
  Purchase #6 $182.30   10.181%   $200.86   $200.86   $200.85   $200.90  
  Purchase #7 $243.59   5.717%   $257.516   $257.52   $257.50   $257.50  
  7 purchase totals = $1,332.25       $1,430.4911   $1,430.50   $1,430.50   $1,430.50