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 $154.35   7.106%   $165.3181   $165.32   $165.30   $165.30  
  Purchase #2 $230.36   10.554%   $254.6722   $254.67   $254.65   $254.70  
  Purchase #3 $219.78   12.559%   $247.3822   $247.38   $247.40   $247.40  
  Purchase #4 $128.58   4.364%   $134.1912   $134.19   $134.20   $134.20  
  Purchase #5 $16.58   12.199%   $18.6026   $18.60   $18.60   $18.60  
  Purchase #6 $139.35   4.210%   $145.2166   $145.22   $145.20   $145.20  
  Purchase #7 $95.26   3.429%   $98.5265   $98.53   $98.55   $98.50  
  7 purchase totals = $984.26       $1,063.9094   $1,063.91   $1,063.90   $1,063.90