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 $232.46   13.146%   $263.0192   $263.02   $263.00   $263.00  
  Purchase #2 $189.80   11.852%   $212.2951   $212.30   $212.30   $212.30  
  Purchase #3 $246.35   12.867%   $278.0479   $278.05   $278.05   $278.00  
  Purchase #4 $138.41   12.501%   $155.7126   $155.71   $155.70   $155.70  
  Purchase #5 $13.94   3.566%   $14.4371   $14.44   $14.45   $14.40  
  Purchase #6 $46.78   9.561%   $51.2526   $51.25   $51.25   $51.30  
  Purchase #7 $15.48   13.554%   $17.5782   $17.58   $17.60   $17.60  
  7 purchase totals = $883.22       $992.3427   $992.35   $992.35   $992.30