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 $91.69   3.148%   $94.5764   $94.58   $94.60   $94.60  
  Purchase #2 $93.55   5.156%   $98.3734   $98.37   $98.35   $98.40  
  Purchase #3 $178.98   4.682%   $187.3598   $187.36   $187.35   $187.40  
  Purchase #4 $162.72   3.219%   $167.958   $167.96   $167.95   $168.00  
  Purchase #5 $247.54   11.406%   $275.7744   $275.77   $275.75   $275.80  
  Purchase #6 $181.98   13.664%   $206.8457   $206.85   $206.85   $206.80  
  Purchase #7 $145.44   4.554%   $152.0633   $152.06   $152.05   $152.10  
  7 purchase totals = $1,101.90       $1,182.9510   $1,182.95   $1,182.90   $1,183.10