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 $61.67   11.219%   $68.5888   $68.59   $68.60   $68.60  
  Purchase #2 $230.43   11.601%   $257.1622   $257.16   $257.15   $257.20  
  Purchase #3 $148.36   13.132%   $167.8426   $167.84   $167.85   $167.80  
  Purchase #4 $166.29   11.738%   $185.8091   $185.81   $185.80   $185.80  
  Purchase #5 $129.39   9.763%   $142.0223   $142.02   $142.00   $142.00  
  Purchase #6 $168.79   6.377%   $179.5537   $179.55   $179.55   $179.60  
  Purchase #7 $203.34   13.697%   $231.1915   $231.19   $231.20   $231.20  
  7 purchase totals = $1,108.27       $1,232.1702   $1,232.16   $1,232.15   $1,232.20