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 $49.59   9.865%   $54.4821   $54.48   $54.50   $54.50  
  Purchase #2 $247.84   9.353%   $271.0205   $271.02   $271.00   $271.00  
  Purchase #3 $88.94   7.432%   $95.55   $95.55   $95.55   $95.60  
  Purchase #4 $96.90   8.122%   $104.7702   $104.77   $104.75   $104.80  
  Purchase #5 $233.67   5.275%   $245.9961   $246.00   $246.00   $246.00  
  Purchase #6 $66.74   5.183%   $70.1991   $70.20   $70.20   $70.20  
  Purchase #7 $80.75   10.836%   $89.5001   $89.50   $89.50   $89.50  
  7 purchase totals = $864.43       $931.5181   $931.52   $931.50   $931.60