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 $61.94   13.616%   $70.3738   $70.37   $70.35   $70.40  
  Purchase #2 $168.44   6.174%   $178.8395   $178.84   $178.85   $178.80  
  Purchase #3 $141.49   5.820%   $149.7247   $149.72   $149.70   $149.70  
  Purchase #4 $202.25   12.511%   $227.5535   $227.55   $227.55   $227.60  
  Purchase #5 $218.28   6.662%   $232.8218   $232.82   $232.80   $232.80  
  Purchase #6 $106.80   8.782%   $116.1792   $116.18   $116.20   $116.20  
  Purchase #7 $183.78   8.559%   $199.5097   $199.51   $199.50   $199.50  
  7 purchase totals = $1,082.98       $1,175.0022   $1,174.99   $1,174.95   $1,175.00