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 $62.33   11.822%   $69.6987   $69.70   $69.70   $69.70  
  Purchase #2 $113.78   6.571%   $121.2565   $121.26   $121.25   $121.30  
  Purchase #3 $96.81   9.170%   $105.6875   $105.69   $105.70   $105.70  
  Purchase #4 $150.29   11.229%   $167.1661   $167.17   $167.15   $167.20  
  Purchase #5 $123.92   13.409%   $140.5364   $140.54   $140.55   $140.50  
  Purchase #6 $239.59   12.349%   $269.177   $269.18   $269.20   $269.20  
  Purchase #7 $70.67   5.456%   $74.5258   $74.53   $74.55   $74.50  
  7 purchase totals = $857.39       $948.0480   $948.07   $948.10   $948.10