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 $216.88   13.284%   $245.6903   $245.69   $245.70   $245.70  
  Purchase #2 $49.96   9.345%   $54.6288   $54.63   $54.65   $54.60  
  Purchase #3 $150.91   3.744%   $156.5601   $156.56   $156.55   $156.60  
  Purchase #4 $139.39   6.515%   $148.4713   $148.47   $148.45   $148.50  
  Purchase #5 $131.26   5.558%   $138.5554   $138.56   $138.55   $138.60  
  Purchase #6 $21.75   11.359%   $24.2206   $24.22   $24.20   $24.20  
  Purchase #7 $233.83   4.367%   $244.0414   $244.04   $244.05   $244.00  
  7 purchase totals = $943.98       $1,012.1679   $1,012.17   $1,012.15   $1,012.20