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 $223.65   8.172%   $241.9267   $241.93   $241.95   $241.90  
  Purchase #2 $100.26   4.419%   $104.6905   $104.69   $104.70   $104.70  
  Purchase #3 $149.59   11.690%   $167.0771   $167.08   $167.10   $167.10  
  Purchase #4 $121.67   6.747%   $129.8791   $129.88   $129.90   $129.90  
  Purchase #5 $151.85   6.553%   $161.8007   $161.80   $161.80   $161.80  
  Purchase #6 $100.83   9.116%   $110.0217   $110.02   $110.00   $110.00  
  Purchase #7 $149.63   12.664%   $168.5791   $168.58   $168.60   $168.60  
  7 purchase totals = $997.48       $1,083.9749   $1,083.98   $1,084.05   $1,084.00