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 $66.69   5.357%   $70.2626   $70.26   $70.25   $70.30  
  Purchase #2 $85.39   4.751%   $89.4469   $89.45   $89.45   $89.40  
  Purchase #3 $216.29   7.656%   $232.8492   $232.85   $232.85   $232.80  
  Purchase #4 $155.41   8.752%   $169.0115   $169.01   $169.00   $169.00  
  Purchase #5 $206.34   10.238%   $227.4651   $227.47   $227.45   $227.50  
  Purchase #6 $51.86   7.123%   $55.554   $55.55   $55.55   $55.60  
  Purchase #7 $186.81   7.794%   $201.37   $201.37   $201.35   $201.40  
  7 purchase totals = $968.79       $1,045.9593   $1,045.96   $1,045.90   $1,046.00