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 $57.49   8.122%   $62.1593   $62.16   $62.15   $62.20  
  Purchase #2 $196.84   11.719%   $219.9077   $219.91   $219.90   $219.90  
  Purchase #3 $33.52   5.466%   $35.3522   $35.35   $35.35   $35.40  
  Purchase #4 $194.57   7.748%   $209.6453   $209.65   $209.65   $209.60  
  Purchase #5 $43.51   5.127%   $45.7408   $45.74   $45.75   $45.70  
  Purchase #6 $22.98   10.555%   $25.4055   $25.41   $25.40   $25.40  
  Purchase #7 $161.75   9.194%   $176.6213   $176.62   $176.60   $176.60  
  7 purchase totals = $710.66       $774.8321   $774.84   $774.80   $774.80