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 $113.53   8.595%   $123.2879   $123.29   $123.30   $123.30  
  Purchase #2 $175.38   6.743%   $187.2059   $187.21   $187.20   $187.20  
  Purchase #3 $64.95   5.869%   $68.7619   $68.76   $68.75   $68.80  
  Purchase #4 $36.97   12.546%   $41.6083   $41.61   $41.60   $41.60  
  Purchase #5 $174.35   11.632%   $194.6304   $194.63   $194.65   $194.60  
  Purchase #6 $155.85   13.198%   $176.4191   $176.42   $176.40   $176.40  
  Purchase #7 $210.80   5.842%   $223.1149   $223.11   $223.10   $223.10  
  7 purchase totals = $931.83       $1,015.0284   $1,015.03   $1,015.00   $1,015.00