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 $191.85   11.539%   $213.9876   $213.99   $214.00   $214.00  
  Purchase #2 $98.96   3.825%   $102.7452   $102.75   $102.75   $102.70  
  Purchase #3 $81.60   10.212%   $89.933   $89.93   $89.95   $89.90  
  Purchase #4 $157.98   5.702%   $166.988   $166.99   $167.00   $167.00  
  Purchase #5 $103.52   3.144%   $106.7747   $106.77   $106.75   $106.80  
  Purchase #6 $151.42   12.648%   $170.5716   $170.57   $170.55   $170.60  
  Purchase #7 $142.38   5.870%   $150.7377   $150.74   $150.75   $150.70  
  7 purchase totals = $927.71       $1,001.7378   $1,001.74   $1,001.75   $1,001.70