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 $198.86   8.374%   $215.5125   $215.51   $215.50   $215.50  
  Purchase #2 $30.96   7.691%   $33.3411   $33.34   $33.35   $33.30  
  Purchase #3 $24.59   9.176%   $26.8464   $26.85   $26.85   $26.80  
  Purchase #4 $123.60   4.356%   $128.984   $128.98   $129.00   $129.00  
  Purchase #5 $235.51   6.218%   $250.154   $250.15   $250.15   $250.20  
  Purchase #6 $51.54   9.379%   $56.3739   $56.37   $56.35   $56.40  
  Purchase #7 $153.89   6.433%   $163.7897   $163.79   $163.80   $163.80  
  7 purchase totals = $818.95       $875.0016   $874.99   $875.00   $875.00