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 $56.25   13.170%   $63.6581   $63.66   $63.65   $63.70  
  Purchase #2 $125.34   12.374%   $140.8496   $140.85   $140.85   $140.80  
  Purchase #3 $192.51   6.406%   $204.8422   $204.84   $204.85   $204.80  
  Purchase #4 $211.38   3.558%   $218.9009   $218.90   $218.90   $218.90  
  Purchase #5 $153.47   7.681%   $165.258   $165.26   $165.25   $165.30  
  Purchase #6 $171.42   3.841%   $178.0042   $178.00   $178.00   $178.00  
  Purchase #7 $29.30   6.376%   $31.1682   $31.17   $31.15   $31.20  
  7 purchase totals = $939.67       $1,002.6812   $1,002.68   $1,002.65   $1,002.70