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 $211.34   10.604%   $233.7505   $233.75   $233.75   $233.80  
  Purchase #2 $149.57   7.375%   $160.6008   $160.60   $160.60   $160.60  
  Purchase #3 $104.84   6.852%   $112.0236   $112.02   $112.00   $112.00  
  Purchase #4 $36.53   7.731%   $39.3541   $39.35   $39.35   $39.40  
  Purchase #5 $191.39   12.779%   $215.8477   $215.85   $215.85   $215.80  
  Purchase #6 $130.40   12.821%   $147.1186   $147.12   $147.10   $147.10  
  Purchase #7 $140.67   12.781%   $158.649   $158.65   $158.65   $158.60  
  7 purchase totals = $964.74       $1,067.3443   $1,067.34   $1,067.30   $1,067.30