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 $75.74   10.409%   $83.6238   $83.62   $83.60   $83.60  
  Purchase #2 $221.29   11.163%   $245.9926   $245.99   $246.00   $246.00  
  Purchase #3 $173.45   5.346%   $182.7226   $182.72   $182.70   $182.70  
  Purchase #4 $182.35   5.446%   $192.2808   $192.28   $192.30   $192.30  
  Purchase #5 $32.84   11.619%   $36.6557   $36.66   $36.65   $36.70  
  Purchase #6 $200.61   8.412%   $217.4853   $217.49   $217.50   $217.50  
  Purchase #7 $112.67   9.664%   $123.5584   $123.56   $123.55   $123.60  
  7 purchase totals = $998.95       $1,082.3192   $1,082.32   $1,082.30   $1,082.40