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 $225.43   6.345%   $239.7335   $239.73   $239.75   $239.70  
  Purchase #2 $179.97   9.851%   $197.6988   $197.70   $197.70   $197.70  
  Purchase #3 $37.93   7.812%   $40.8931   $40.89   $40.90   $40.90  
  Purchase #4 $134.45   7.848%   $145.0016   $145.00   $145.00   $145.00  
  Purchase #5 $119.48   10.753%   $132.3277   $132.33   $132.35   $132.30  
  Purchase #6 $200.64   6.532%   $213.7458   $213.75   $213.75   $213.70  
  Purchase #7 $51.93   7.844%   $56.0034   $56.00   $56.00   $56.00  
  7 purchase totals = $949.83       $1,025.4039   $1,025.40   $1,025.45   $1,025.30