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 $244.93   8.558%   $265.8911   $265.89   $265.90   $265.90  
  Purchase #2 $91.40   5.852%   $96.7487   $96.75   $96.75   $96.70  
  Purchase #3 $215.43   11.621%   $240.4651   $240.47   $240.45   $240.50  
  Purchase #4 $116.58   13.708%   $132.5608   $132.56   $132.55   $132.60  
  Purchase #5 $129.68   9.518%   $142.0229   $142.02   $142.00   $142.00  
  Purchase #6 $31.51   9.607%   $34.5372   $34.54   $34.55   $34.50  
  Purchase #7 $163.33   7.820%   $176.1024   $176.10   $176.10   $176.10  
  7 purchase totals = $992.86       $1,088.3282   $1,088.33   $1,088.30   $1,088.30