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 $186.58   11.471%   $207.9826   $207.98   $208.00   $208.00  
  Purchase #2 $116.26   12.684%   $131.0064   $131.01   $131.00   $131.00  
  Purchase #3 $65.96   8.126%   $71.3199   $71.32   $71.30   $71.30  
  Purchase #4 $133.35   8.831%   $145.1261   $145.13   $145.15   $145.10  
  Purchase #5 $249.32   5.823%   $263.8379   $263.84   $263.85   $263.80  
  Purchase #6 $128.90   8.862%   $140.3231   $140.32   $140.30   $140.30  
  Purchase #7 $119.99   13.262%   $135.9031   $135.90   $135.90   $135.90  
  7 purchase totals = $1,000.36       $1,095.4991   $1,095.50   $1,095.50   $1,095.40