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 $93.49   8.663%   $101.589   $101.59   $101.60   $101.60  
  Purchase #2 $102.51   7.285%   $109.9779   $109.98   $110.00   $110.00  
  Purchase #3 $15.95   8.426%   $17.2939   $17.29   $17.30   $17.30  
  Purchase #4 $191.48   12.730%   $215.8554   $215.86   $215.85   $215.90  
  Purchase #5 $101.27   8.807%   $110.1888   $110.19   $110.20   $110.20  
  Purchase #6 $165.58   4.541%   $173.099   $173.10   $173.10   $173.10  
  Purchase #7 $64.66   9.704%   $70.9346   $70.93   $70.95   $70.90  
  7 purchase totals = $734.94       $798.9386   $798.94   $799.00   $799.00