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 $114.57   7.559%   $123.2303   $123.23   $123.25   $123.20  
  Purchase #2 $248.93   3.299%   $257.1422   $257.14   $257.15   $257.10  
  Purchase #3 $171.79   12.290%   $192.903   $192.90   $192.90   $192.90  
  Purchase #4 $36.99   6.297%   $39.3193   $39.32   $39.30   $39.30  
  Purchase #5 $8.29   6.815%   $8.855   $8.86   $8.85   $8.90  
  Purchase #6 $199.60   9.416%   $218.3943   $218.39   $218.40   $218.40  
  Purchase #7 $65.88   6.217%   $69.9758   $69.98   $70.00   $70.00  
  7 purchase totals = $846.05       $909.8199   $909.82   $909.85   $909.80