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 $15.47   11.310%   $17.2197   $17.22   $17.20   $17.20  
  Purchase #2 $204.39   3.745%   $212.0444   $212.04   $212.05   $212.00  
  Purchase #3 $91.86   4.691%   $96.1692   $96.17   $96.15   $96.20  
  Purchase #4 $152.34   3.496%   $157.6658   $157.67   $157.65   $157.70  
  Purchase #5 $96.61   13.460%   $109.6137   $109.61   $109.60   $109.60  
  Purchase #6 $150.55   9.735%   $165.206   $165.21   $165.20   $165.20  
  Purchase #7 $232.74   13.853%   $264.9815   $264.98   $265.00   $265.00  
  7 purchase totals = $943.96       $1,022.9003   $1,022.90   $1,022.85   $1,022.90