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 $47.65   8.164%   $51.5401   $51.54   $51.55   $51.50  
  Purchase #2 $219.43   4.176%   $228.5934   $228.59   $228.60   $228.60  
  Purchase #3 $240.37   12.445%   $270.284   $270.28   $270.30   $270.30  
  Purchase #4 $100.65   5.344%   $106.0287   $106.03   $106.05   $106.00  
  Purchase #5 $231.84   9.143%   $253.0371   $253.04   $253.05   $253.00  
  Purchase #6 $204.96   9.620%   $224.6772   $224.68   $224.70   $224.70  
  Purchase #7 $124.78   12.867%   $140.8354   $140.84   $140.85   $140.80  
  7 purchase totals = $1,169.68       $1,274.9959   $1,275.00   $1,275.10   $1,274.90