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 $58.74   11.784%   $65.6619   $65.66   $65.65   $65.70  
  Purchase #2 $226.87   6.570%   $241.7754   $241.78   $241.80   $241.80  
  Purchase #3 $194.70   12.634%   $219.2984   $219.30   $219.30   $219.30  
  Purchase #4 $208.63   11.491%   $232.6037   $232.60   $232.60   $232.60  
  Purchase #5 $113.75   7.188%   $121.9264   $121.93   $121.95   $121.90  
  Purchase #6 $190.28   10.545%   $210.345   $210.35   $210.35   $210.30  
  Purchase #7 $87.65   9.124%   $95.6472   $95.65   $95.65   $95.60  
  7 purchase totals = $1,080.62       $1,187.2580   $1,187.27   $1,187.30   $1,187.20