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 $232.72   10.725%   $257.6792   $257.68   $257.70   $257.70  
  Purchase #2 $149.63   13.392%   $169.6684   $169.67   $169.65   $169.70  
  Purchase #3 $172.65   4.236%   $179.9635   $179.96   $179.95   $180.00  
  Purchase #4 $151.64   7.319%   $162.7385   $162.74   $162.75   $162.70  
  Purchase #5 $235.99   12.864%   $266.3478   $266.35   $266.35   $266.30  
  Purchase #6 $193.92   5.150%   $203.9069   $203.91   $203.90   $203.90  
  Purchase #7 $96.58   9.125%   $105.3929   $105.39   $105.40   $105.40  
  7 purchase totals = $1,233.13       $1,345.6972   $1,345.70   $1,345.70   $1,345.70