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 $69.91   3.457%   $72.3268   $72.33   $72.35   $72.30  
  Purchase #2 $250.41   13.313%   $283.7471   $283.75   $283.75   $283.70  
  Purchase #3 $169.61   7.435%   $182.2205   $182.22   $182.20   $182.20  
  Purchase #4 $92.52   10.642%   $102.366   $102.37   $102.35   $102.40  
  Purchase #5 $162.99   13.399%   $184.829   $184.83   $184.85   $184.80  
  Purchase #6 $223.90   11.241%   $249.0686   $249.07   $249.05   $249.10  
  Purchase #7 $160.45   12.516%   $180.5319   $180.53   $180.55   $180.50  
  7 purchase totals = $1,129.79       $1,255.0899   $1,255.10   $1,255.10   $1,255.00