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 $127.67   13.726%   $145.194   $145.19   $145.20   $145.20  
  Purchase #2 $140.84   8.634%   $153.0001   $153.00   $153.00   $153.00  
  Purchase #3 $76.45   3.598%   $79.2007   $79.20   $79.20   $79.20  
  Purchase #4 $186.84   9.238%   $204.1003   $204.10   $204.10   $204.10  
  Purchase #5 $184.32   9.529%   $201.8839   $201.88   $201.90   $201.90  
  Purchase #6 $154.91   11.110%   $172.1205   $172.12   $172.10   $172.10  
  Purchase #7 $95.62   13.707%   $108.7266   $108.73   $108.75   $108.70  
  7 purchase totals = $966.65       $1,064.2261   $1,064.22   $1,064.25   $1,064.20