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 $201.92   12.598%   $227.3579   $227.36   $227.35   $227.40  
  Purchase #2 $210.54   5.254%   $221.6018   $221.60   $221.60   $221.60  
  Purchase #3 $128.91   5.621%   $136.156   $136.16   $136.15   $136.20  
  Purchase #4 $16.43   7.786%   $17.7092   $17.71   $17.70   $17.70  
  Purchase #5 $226.88   5.864%   $240.1842   $240.18   $240.20   $240.20  
  Purchase #6 $112.67   5.503%   $118.8702   $118.87   $118.85   $118.90  
  Purchase #7 $56.31   6.585%   $60.018   $60.02   $60.00   $60.00  
  7 purchase totals = $953.66       $1,021.8973   $1,021.90   $1,021.85   $1,022.00