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 $246.53   10.819%   $273.2021   $273.20   $273.20   $273.20  
  Purchase #2 $36.79   13.452%   $41.739   $41.74   $41.75   $41.70  
  Purchase #3 $189.68   8.488%   $205.78   $205.78   $205.80   $205.80  
  Purchase #4 $54.55   10.195%   $60.1114   $60.11   $60.10   $60.10  
  Purchase #5 $110.30   9.405%   $120.6737   $120.67   $120.65   $120.70  
  Purchase #6 $126.80   8.327%   $137.3586   $137.36   $137.35   $137.40  
  Purchase #7 $187.84   3.852%   $195.0756   $195.08   $195.10   $195.10  
  7 purchase totals = $952.49       $1,033.9404   $1,033.94   $1,033.95   $1,034.00