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 $216.85   6.319%   $230.5528   $230.55   $230.55   $230.60  
  Purchase #2 $203.90   6.346%   $216.8395   $216.84   $216.85   $216.80  
  Purchase #3 $77.90   7.111%   $83.4395   $83.44   $83.45   $83.40  
  Purchase #4 $36.71   9.150%   $40.069   $40.07   $40.05   $40.10  
  Purchase #5 $39.84   13.281%   $45.1312   $45.13   $45.15   $45.10  
  Purchase #6 $95.92   12.576%   $107.9829   $107.98   $108.00   $108.00  
  Purchase #7 $225.74   7.278%   $242.1694   $242.17   $242.15   $242.20  
  7 purchase totals = $896.86       $966.1843   $966.18   $966.20   $966.20