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 $86.57   13.331%   $98.1106   $98.11   $98.10   $98.10  
  Purchase #2 $126.77   6.464%   $134.9644   $134.96   $134.95   $135.00  
  Purchase #3 $244.72   5.759%   $258.8134   $258.81   $258.80   $258.80  
  Purchase #4 $149.73   12.116%   $167.8713   $167.87   $167.85   $167.90  
  Purchase #5 $143.99   6.389%   $153.1895   $153.19   $153.20   $153.20  
  Purchase #6 $148.55   3.376%   $153.565   $153.57   $153.55   $153.60  
  Purchase #7 $54.44   10.488%   $60.1497   $60.15   $60.15   $60.10  
  7 purchase totals = $954.77       $1,026.6639   $1,026.66   $1,026.60   $1,026.70