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 $43.72   9.512%   $47.8786   $47.88   $47.90   $47.90  
  Purchase #2 $212.54   6.487%   $226.3275   $226.33   $226.35   $226.30  
  Purchase #3 $242.89   8.400%   $263.2928   $263.29   $263.30   $263.30  
  Purchase #4 $24.59   8.459%   $26.6701   $26.67   $26.65   $26.70  
  Purchase #5 $230.92   7.679%   $248.6523   $248.65   $248.65   $248.70  
  Purchase #6 $234.84   6.555%   $250.2338   $250.23   $250.25   $250.20  
  Purchase #7 $160.37   4.144%   $167.0157   $167.02   $167.00   $167.00  
  7 purchase totals = $1,149.87       $1,230.0708   $1,230.07   $1,230.10   $1,230.10