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 $153.39   8.224%   $166.0048   $166.00   $166.00   $166.00  
  Purchase #2 $184.64   5.596%   $194.9725   $194.97   $194.95   $195.00  
  Purchase #3 $162.98   6.300%   $173.2477   $173.25   $173.25   $173.20  
  Purchase #4 $98.37   3.656%   $101.9664   $101.97   $101.95   $102.00  
  Purchase #5 $72.93   10.809%   $80.813   $80.81   $80.80   $80.80  
  Purchase #6 $130.88   7.542%   $140.751   $140.75   $140.75   $140.80  
  Purchase #7 $142.73   9.750%   $156.6462   $156.65   $156.65   $156.60  
  7 purchase totals = $945.92       $1,014.4016   $1,014.40   $1,014.35   $1,014.40