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 $151.67   8.229%   $164.1509   $164.15   $164.15   $164.20  
  Purchase #2 $108.31   10.762%   $119.9663   $119.97   $119.95   $120.00  
  Purchase #3 $195.82   3.673%   $203.0125   $203.01   $203.00   $203.00  
  Purchase #4 $164.73   5.486%   $173.7671   $173.77   $173.75   $173.80  
  Purchase #5 $172.26   7.168%   $184.6076   $184.61   $184.60   $184.60  
  Purchase #6 $32.29   10.142%   $35.5649   $35.56   $35.55   $35.60  
  Purchase #7 $135.63   6.739%   $144.7701   $144.77   $144.75   $144.80  
  7 purchase totals = $960.71       $1,025.8394   $1,025.84   $1,025.75   $1,026.00