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 $248.62   7.473%   $267.1994   $267.20   $267.20   $267.20  
  Purchase #2 $191.55   10.478%   $211.6206   $211.62   $211.60   $211.60  
  Purchase #3 $24.85   11.297%   $27.6573   $27.66   $27.65   $27.70  
  Purchase #4 $166.96   5.465%   $176.0844   $176.08   $176.10   $176.10  
  Purchase #5 $46.29   10.398%   $51.1032   $51.10   $51.10   $51.10  
  Purchase #6 $64.57   5.710%   $68.2569   $68.26   $68.25   $68.30  
  Purchase #7 $205.59   6.149%   $218.2317   $218.23   $218.25   $218.20  
  7 purchase totals = $948.43       $1,020.1535   $1,020.15   $1,020.15   $1,020.20