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 $238.65   13.221%   $270.2019   $270.20   $270.20   $270.20  
  Purchase #2 $248.96   13.608%   $282.8385   $282.84   $282.85   $282.80  
  Purchase #3 $94.88   5.649%   $100.2398   $100.24   $100.25   $100.20  
  Purchase #4 $26.87   9.343%   $29.3805   $29.38   $29.40   $29.40  
  Purchase #5 $203.37   5.590%   $214.7384   $214.74   $214.75   $214.70  
  Purchase #6 $204.92   10.542%   $226.5227   $226.52   $226.50   $226.50  
  Purchase #7 $107.59   4.736%   $112.6855   $112.69   $112.70   $112.70  
  7 purchase totals = $1,125.24       $1,236.6073   $1,236.61   $1,236.65   $1,236.50