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 $144.83   10.296%   $159.7417   $159.74   $159.75   $159.70  
  Purchase #2 $145.63   4.370%   $151.994   $151.99   $152.00   $152.00  
  Purchase #3 $155.46   5.713%   $164.3414   $164.34   $164.35   $164.30  
  Purchase #4 $194.64   12.519%   $219.007   $219.01   $219.00   $219.00  
  Purchase #5 $76.96   7.359%   $82.6235   $82.62   $82.60   $82.60  
  Purchase #6 $121.64   5.841%   $128.745   $128.75   $128.75   $128.70  
  Purchase #7 $106.86   10.744%   $118.341   $118.34   $118.35   $118.30  
  7 purchase totals = $946.02       $1,024.7936   $1,024.79   $1,024.80   $1,024.60