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 $204.84   4.464%   $213.9841   $213.98   $214.00   $214.00  
  Purchase #2 $142.69   13.194%   $161.5165   $161.52   $161.50   $161.50  
  Purchase #3 $167.63   11.839%   $187.4757   $187.48   $187.50   $187.50  
  Purchase #4 $104.87   4.844%   $109.9499   $109.95   $109.95   $109.90  
  Purchase #5 $114.49   3.471%   $118.4639   $118.46   $118.45   $118.50  
  Purchase #6 $73.80   11.568%   $82.3372   $82.34   $82.35   $82.30  
  Purchase #7 $124.54   8.379%   $134.9752   $134.98   $135.00   $135.00  
  7 purchase totals = $932.86       $1,008.7025   $1,008.71   $1,008.75   $1,008.70