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 $124.67   7.649%   $134.206   $134.21   $134.20   $134.20  
  Purchase #2 $139.30   11.735%   $155.6469   $155.65   $155.65   $155.60  
  Purchase #3 $138.29   3.693%   $143.397   $143.40   $143.40   $143.40  
  Purchase #4 $67.56   10.601%   $74.722   $74.72   $74.70   $74.70  
  Purchase #5 $198.85   11.442%   $221.6024   $221.60   $221.60   $221.60  
  Purchase #6 $139.67   6.712%   $149.0447   $149.04   $149.05   $149.00  
  Purchase #7 $137.88   11.752%   $154.0837   $154.08   $154.10   $154.10  
  7 purchase totals = $946.22       $1,032.7027   $1,032.70   $1,032.70   $1,032.60