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 $243.98   12.349%   $274.1091   $274.11   $274.10   $274.10  
  Purchase #2 $141.74   12.114%   $158.9104   $158.91   $158.90   $158.90  
  Purchase #3 $154.88   8.288%   $167.7165   $167.72   $167.70   $167.70  
  Purchase #4 $141.95   13.194%   $160.6789   $160.68   $160.70   $160.70  
  Purchase #5 $225.58   12.717%   $254.267   $254.27   $254.25   $254.30  
  Purchase #6 $87.46   7.146%   $93.7099   $93.71   $93.70   $93.70  
  Purchase #7 $49.32   7.853%   $53.1931   $53.19   $53.20   $53.20  
  7 purchase totals = $1,044.91       $1,162.5849   $1,162.59   $1,162.55   $1,162.60