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 $73.94   3.159%   $76.2758   $76.28   $76.30   $76.30  
  Purchase #2 $149.67   13.505%   $169.8829   $169.88   $169.90   $169.90  
  Purchase #3 $168.32   7.749%   $181.3631   $181.36   $181.35   $181.40  
  Purchase #4 $202.43   7.749%   $218.1163   $218.12   $218.10   $218.10  
  Purchase #5 $220.48   3.267%   $227.6831   $227.68   $227.70   $227.70  
  Purchase #6 $199.81   11.352%   $222.4924   $222.49   $222.50   $222.50  
  Purchase #7 $142.72   5.808%   $151.0092   $151.01   $151.00   $151.00  
  7 purchase totals = $1,157.37       $1,246.8228   $1,246.82   $1,246.85   $1,246.90