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 $245.72   8.427%   $266.4268   $266.43   $266.45   $266.40  
  Purchase #2 $76.68   13.722%   $87.202   $87.20   $87.20   $87.20  
  Purchase #3 $58.85   11.530%   $65.6354   $65.64   $65.65   $65.60  
  Purchase #4 $217.95   7.161%   $233.5574   $233.56   $233.55   $233.60  
  Purchase #5 $248.51   9.159%   $271.271   $271.27   $271.25   $271.30  
  Purchase #6 $145.43   4.712%   $152.2827   $152.28   $152.30   $152.30  
  Purchase #7 $95.80   4.125%   $99.7518   $99.75   $99.75   $99.80  
  7 purchase totals = $1,088.94       $1,176.1271   $1,176.13   $1,176.15   $1,176.20