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 $165.75   11.192%   $184.3007   $184.30   $184.30   $184.30  
  Purchase #2 $47.64   12.553%   $53.6202   $53.62   $53.60   $53.60  
  Purchase #3 $132.77   11.202%   $147.6429   $147.64   $147.65   $147.60  
  Purchase #4 $106.37   9.506%   $116.4815   $116.48   $116.50   $116.50  
  Purchase #5 $75.70   6.765%   $80.8211   $80.82   $80.80   $80.80  
  Purchase #6 $242.62   13.823%   $276.1574   $276.16   $276.15   $276.20  
  Purchase #7 $234.54   3.268%   $242.2048   $242.20   $242.20   $242.20  
  7 purchase totals = $1,005.39       $1,101.2286   $1,101.22   $1,101.20   $1,101.20