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 $38.33   12.787%   $43.2313   $43.23   $43.25   $43.20  
  Purchase #2 $247.72   6.478%   $263.7673   $263.77   $263.75   $263.80  
  Purchase #3 $149.48   10.548%   $165.2472   $165.25   $165.25   $165.20  
  Purchase #4 $219.54   6.846%   $234.5697   $234.57   $234.55   $234.60  
  Purchase #5 $141.28   13.552%   $160.4263   $160.43   $160.45   $160.40  
  Purchase #6 $78.33   8.404%   $84.9129   $84.91   $84.90   $84.90  
  Purchase #7 $53.29   5.209%   $56.0659   $56.07   $56.05   $56.10  
  7 purchase totals = $927.97       $1,008.2206   $1,008.23   $1,008.20   $1,008.20