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 $245.77   6.746%   $262.3496   $262.35   $262.35   $262.30  
  Purchase #2 $132.92   4.620%   $139.0609   $139.06   $139.05   $139.10  
  Purchase #3 $147.75   13.322%   $167.4333   $167.43   $167.45   $167.40  
  Purchase #4 $32.30   13.728%   $36.7341   $36.73   $36.75   $36.70  
  Purchase #5 $104.59   3.653%   $108.4107   $108.41   $108.40   $108.40  
  Purchase #6 $206.82   12.562%   $232.8007   $232.80   $232.80   $232.80  
  Purchase #7 $60.43   7.123%   $64.7344   $64.73   $64.75   $64.70  
  7 purchase totals = $930.58       $1,011.5237   $1,011.51   $1,011.55   $1,011.40