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 $156.48   12.737%   $176.4109   $176.41   $176.40   $176.40  
  Purchase #2 $243.86   9.844%   $267.8656   $267.87   $267.85   $267.90  
  Purchase #3 $179.56   9.873%   $197.288   $197.29   $197.30   $197.30  
  Purchase #4 $27.40   7.209%   $29.3753   $29.38   $29.40   $29.40  
  Purchase #5 $57.74   8.114%   $62.425   $62.43   $62.45   $62.40  
  Purchase #6 $169.29   10.822%   $187.6106   $187.61   $187.60   $187.60  
  Purchase #7 $211.53   13.830%   $240.7846   $240.78   $240.80   $240.80  
  7 purchase totals = $1,045.86       $1,161.7600   $1,161.77   $1,161.80   $1,161.80