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 $96.34   13.162%   $109.0203   $109.02   $109.00   $109.00  
  Purchase #2 $158.33   11.609%   $176.7105   $176.71   $176.70   $176.70  
  Purchase #3 $179.83   7.484%   $193.2885   $193.29   $193.30   $193.30  
  Purchase #4 $104.67   3.470%   $108.302   $108.30   $108.30   $108.30  
  Purchase #5 $139.32   8.263%   $150.832   $150.83   $150.85   $150.80  
  Purchase #6 $11.91   5.557%   $12.5718   $12.57   $12.55   $12.60  
  Purchase #7 $10.98   5.806%   $11.6175   $11.62   $11.60   $11.60  
  7 purchase totals = $701.38       $762.3426   $762.34   $762.30   $762.30