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 $61.46   8.305%   $66.5643   $66.56   $66.55   $66.60  
  Purchase #2 $244.47   6.530%   $260.4339   $260.43   $260.45   $260.40  
  Purchase #3 $238.43   3.135%   $245.9048   $245.90   $245.90   $245.90  
  Purchase #4 $128.96   4.841%   $135.203   $135.20   $135.20   $135.20  
  Purchase #5 $164.69   7.195%   $176.5394   $176.54   $176.55   $176.50  
  Purchase #6 $115.56   3.826%   $119.9813   $119.98   $120.00   $120.00  
  Purchase #7 $167.79   11.316%   $186.7771   $186.78   $186.80   $186.80  
  7 purchase totals = $1,121.36       $1,191.4038   $1,191.39   $1,191.45   $1,191.40