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 $58.59   8.864%   $63.7834   $63.78   $63.80   $63.80  
  Purchase #2 $223.51   10.810%   $247.6714   $247.67   $247.65   $247.70  
  Purchase #3 $30.55   6.517%   $32.5409   $32.54   $32.55   $32.50  
  Purchase #4 $94.54   8.732%   $102.7952   $102.80   $102.80   $102.80  
  Purchase #5 $94.90   12.104%   $106.3867   $106.39   $106.40   $106.40  
  Purchase #6 $161.96   3.527%   $167.6723   $167.67   $167.65   $167.70  
  Purchase #7 $158.88   9.102%   $173.3413   $173.34   $173.35   $173.30  
  7 purchase totals = $822.93       $894.1912   $894.19   $894.20   $894.20