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 $238.70   9.249%   $260.7774   $260.78   $260.80   $260.80  
  Purchase #2 $116.75   9.284%   $127.5891   $127.59   $127.60   $127.60  
  Purchase #3 $59.64   7.788%   $64.2848   $64.28   $64.30   $64.30  
  Purchase #4 $212.79   3.734%   $220.7356   $220.74   $220.75   $220.70  
  Purchase #5 $8.77   4.203%   $9.1386   $9.14   $9.15   $9.10  
  Purchase #6 $71.94   5.469%   $75.8744   $75.87   $75.85   $75.90  
  Purchase #7 $190.95   11.553%   $213.0105   $213.01   $213.00   $213.00  
  7 purchase totals = $899.54       $971.4104   $971.41   $971.45   $971.40