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 $174.41   6.625%   $185.9647   $185.96   $185.95   $186.00  
  Purchase #2 $202.72   11.441%   $225.9132   $225.91   $225.90   $225.90  
  Purchase #3 $151.51   10.599%   $167.5685   $167.57   $167.55   $167.60  
  Purchase #4 $205.35   7.234%   $220.205   $220.21   $220.20   $220.20  
  Purchase #5 $54.59   5.479%   $57.581   $57.58   $57.60   $57.60  
  Purchase #6 $246.66   5.560%   $260.3743   $260.37   $260.35   $260.40  
  Purchase #7 $146.88   10.151%   $161.7898   $161.79   $161.80   $161.80  
  7 purchase totals = $1,182.12       $1,279.3965   $1,279.39   $1,279.35   $1,279.50