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 $63.46   6.417%   $67.5322   $67.53   $67.55   $67.50  
  Purchase #2 $221.74   11.349%   $246.9053   $246.91   $246.90   $246.90  
  Purchase #3 $148.51   12.777%   $167.4851   $167.49   $167.50   $167.50  
  Purchase #4 $29.84   7.446%   $32.0619   $32.06   $32.05   $32.10  
  Purchase #5 $152.35   9.119%   $166.2428   $166.24   $166.25   $166.20  
  Purchase #6 $129.77   8.264%   $140.4942   $140.49   $140.50   $140.50  
  Purchase #7 $172.96   4.303%   $180.4025   $180.40   $180.40   $180.40  
  7 purchase totals = $918.63       $1,001.1240   $1,001.12   $1,001.15   $1,001.10