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 $128.49   12.610%   $144.6926   $144.69   $144.70   $144.70  
  Purchase #2 $163.97   12.316%   $184.1645   $184.16   $184.15   $184.20  
  Purchase #3 $240.94   9.367%   $263.5088   $263.51   $263.50   $263.50  
  Purchase #4 $178.95   6.440%   $190.4744   $190.47   $190.45   $190.50  
  Purchase #5 $88.37   8.624%   $95.991   $95.99   $96.00   $96.00  
  Purchase #6 $157.29   11.188%   $174.8876   $174.89   $174.90   $174.90  
  Purchase #7 $37.75   11.240%   $41.9931   $41.99   $42.00   $42.00  
  7 purchase totals = $995.76       $1,095.7120   $1,095.70   $1,095.70   $1,095.80