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 $246.48   8.171%   $266.6199   $266.62   $266.60   $266.60  
  Purchase #2 $57.31   8.692%   $62.2914   $62.29   $62.30   $62.30  
  Purchase #3 $98.66   10.163%   $108.6868   $108.69   $108.70   $108.70  
  Purchase #4 $52.68   9.332%   $57.5961   $57.60   $57.60   $57.60  
  Purchase #5 $204.70   3.544%   $211.9546   $211.95   $211.95   $212.00  
  Purchase #6 $50.77   11.735%   $56.7279   $56.73   $56.75   $56.70  
  Purchase #7 $240.32   7.474%   $258.2815   $258.28   $258.30   $258.30  
  7 purchase totals = $950.92       $1,022.1582   $1,022.16   $1,022.20   $1,022.20