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 $241.53   5.143%   $253.9519   $253.95   $253.95   $254.00  
  Purchase #2 $239.89   9.645%   $263.0274   $263.03   $263.05   $263.00  
  Purchase #3 $228.26   4.596%   $238.7508   $238.75   $238.75   $238.80  
  Purchase #4 $243.63   11.867%   $272.5416   $272.54   $272.55   $272.50  
  Purchase #5 $43.95   7.496%   $47.2445   $47.24   $47.25   $47.20  
  Purchase #6 $120.37   13.222%   $136.2853   $136.29   $136.30   $136.30  
  Purchase #7 $154.94   6.264%   $164.6454   $164.65   $164.65   $164.60  
  7 purchase totals = $1,272.57       $1,376.4469   $1,376.45   $1,376.50   $1,376.40