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 $153.45   13.399%   $174.0108   $174.01   $174.00   $174.00  
  Purchase #2 $169.84   8.431%   $184.1592   $184.16   $184.15   $184.20  
  Purchase #3 $164.41   12.256%   $184.5601   $184.56   $184.55   $184.60  
  Purchase #4 $191.42   5.323%   $201.6093   $201.61   $201.60   $201.60  
  Purchase #5 $88.64   4.751%   $92.8513   $92.85   $92.85   $92.90  
  Purchase #6 $245.75   11.771%   $274.6772   $274.68   $274.70   $274.70  
  Purchase #7 $152.78   6.249%   $162.3272   $162.33   $162.35   $162.30  
  7 purchase totals = $1,166.29       $1,274.1951   $1,274.20   $1,274.20   $1,274.30