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 $191.40   12.857%   $216.0083   $216.01   $216.00   $216.00  
  Purchase #2 $138.75   11.111%   $154.1665   $154.17   $154.15   $154.20  
  Purchase #3 $126.43   3.588%   $130.9663   $130.97   $130.95   $131.00  
  Purchase #4 $179.86   3.472%   $186.1047   $186.10   $186.10   $186.10  
  Purchase #5 $165.25   11.464%   $184.1943   $184.19   $184.20   $184.20  
  Purchase #6 $230.58   11.664%   $257.4749   $257.47   $257.45   $257.50  
  Purchase #7 $64.58   10.485%   $71.3512   $71.35   $71.35   $71.40  
  7 purchase totals = $1,096.85       $1,200.2662   $1,200.26   $1,200.20   $1,200.40