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 $55.65   7.668%   $59.9172   $59.92   $59.90   $59.90  
  Purchase #2 $196.67   8.721%   $213.8216   $213.82   $213.80   $213.80  
  Purchase #3 $8.36   5.713%   $8.8376   $8.84   $8.85   $8.80  
  Purchase #4 $46.44   7.151%   $49.7609   $49.76   $49.75   $49.80  
  Purchase #5 $49.99   10.665%   $55.3214   $55.32   $55.30   $55.30  
  Purchase #6 $165.80   6.265%   $176.1874   $176.19   $176.20   $176.20  
  Purchase #7 $197.27   3.410%   $203.9969   $204.00   $204.00   $204.00  
  7 purchase totals = $720.18       $767.8430   $767.85   $767.80   $767.80