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 $83.41   5.554%   $88.0426   $88.04   $88.05   $88.00  
  Purchase #2 $160.37   8.284%   $173.6551   $173.66   $173.65   $173.70  
  Purchase #3 $164.26   11.342%   $182.8904   $182.89   $182.90   $182.90  
  Purchase #4 $186.81   4.837%   $195.846   $195.85   $195.85   $195.80  
  Purchase #5 $233.42   6.284%   $248.0881   $248.09   $248.10   $248.10  
  Purchase #6 $157.66   6.385%   $167.7266   $167.73   $167.75   $167.70  
  Purchase #7 $12.39   12.795%   $13.9753   $13.98   $14.00   $14.00  
  7 purchase totals = $998.32       $1,070.2241   $1,070.24   $1,070.30   $1,070.20