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 $8.40   4.781%   $8.8016   $8.80   $8.80   $8.80  
  Purchase #2 $143.57   13.780%   $163.3539   $163.35   $163.35   $163.40  
  Purchase #3 $138.92   7.350%   $149.1306   $149.13   $149.15   $149.10  
  Purchase #4 $144.57   3.110%   $149.0661   $149.07   $149.05   $149.10  
  Purchase #5 $227.78   5.539%   $240.3967   $240.40   $240.40   $240.40  
  Purchase #6 $101.73   4.738%   $106.55   $106.55   $106.55   $106.60  
  Purchase #7 $193.82   10.284%   $213.7524   $213.75   $213.75   $213.80  
  7 purchase totals = $958.79       $1,031.0513   $1,031.05   $1,031.05   $1,031.20