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 $219.62   11.111%   $244.022   $244.02   $244.00   $244.00  
  Purchase #2 $134.74   13.394%   $152.7871   $152.79   $152.80   $152.80  
  Purchase #3 $147.42   8.511%   $159.9669   $159.97   $159.95   $160.00  
  Purchase #4 $57.91   11.239%   $64.4185   $64.42   $64.40   $64.40  
  Purchase #5 $26.78   11.847%   $29.9526   $29.95   $29.95   $30.00  
  Purchase #6 $156.57   8.862%   $170.4452   $170.45   $170.45   $170.40  
  Purchase #7 $135.44   13.507%   $153.7339   $153.73   $153.75   $153.70  
  7 purchase totals = $878.48       $975.3262   $975.33   $975.30   $975.30