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 $92.95   11.174%   $103.3362   $103.34   $103.35   $103.30  
  Purchase #2 $53.36   8.232%   $57.7526   $57.75   $57.75   $57.80  
  Purchase #3 $128.54   3.689%   $133.2818   $133.28   $133.30   $133.30  
  Purchase #4 $238.72   12.512%   $268.5886   $268.59   $268.60   $268.60  
  Purchase #5 $189.50   5.241%   $199.4317   $199.43   $199.45   $199.40  
  Purchase #6 $49.73   13.317%   $56.3525   $56.35   $56.35   $56.40  
  Purchase #7 $207.49   11.231%   $230.7932   $230.79   $230.80   $230.80  
  7 purchase totals = $960.29       $1,049.5366   $1,049.53   $1,049.60   $1,049.60