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 $73.30   3.111%   $75.5804   $75.58   $75.60   $75.60  
  Purchase #2 $23.94   8.506%   $25.9763   $25.98   $26.00   $26.00  
  Purchase #3 $96.56   11.721%   $107.8778   $107.88   $107.90   $107.90  
  Purchase #4 $171.74   6.121%   $182.2522   $182.25   $182.25   $182.30  
  Purchase #5 $201.59   9.130%   $219.9952   $220.00   $220.00   $220.00  
  Purchase #6 $122.31   6.531%   $130.2981   $130.30   $130.30   $130.30  
  Purchase #7 $188.46   5.538%   $198.8969   $198.90   $198.90   $198.90  
  7 purchase totals = $877.90       $940.8769   $940.89   $940.95   $941.00