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 $120.81   4.363%   $126.0809   $126.08   $126.10   $126.10  
  Purchase #2 $195.80   8.724%   $212.8816   $212.88   $212.90   $212.90  
  Purchase #3 $154.37   7.511%   $165.9647   $165.96   $165.95   $166.00  
  Purchase #4 $29.94   9.117%   $32.6696   $32.67   $32.65   $32.70  
  Purchase #5 $213.86   8.807%   $232.6947   $232.69   $232.70   $232.70  
  Purchase #6 $244.61   8.456%   $265.2942   $265.29   $265.30   $265.30  
  Purchase #7 $172.25   8.435%   $186.7793   $186.78   $186.80   $186.80  
  7 purchase totals = $1,131.64       $1,222.3650   $1,222.35   $1,222.40   $1,222.50