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 $236.35   13.184%   $267.5104   $267.51   $267.50   $267.50  
  Purchase #2 $5.58   10.687%   $6.1763   $6.18   $6.20   $6.20  
  Purchase #3 $139.30   3.167%   $143.7116   $143.71   $143.70   $143.70  
  Purchase #4 $62.30   11.160%   $69.2527   $69.25   $69.25   $69.30  
  Purchase #5 $193.29   5.514%   $203.948   $203.95   $203.95   $203.90  
  Purchase #6 $148.51   12.595%   $167.2148   $167.21   $167.20   $167.20  
  Purchase #7 $190.90   11.413%   $212.6874   $212.69   $212.70   $212.70  
  7 purchase totals = $976.23       $1,070.5012   $1,070.50   $1,070.50   $1,070.50