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 $90.44   4.651%   $94.6464   $94.65   $94.65   $94.60  
  Purchase #2 $182.44   4.342%   $190.3615   $190.36   $190.35   $190.40  
  Purchase #3 $193.92   9.415%   $212.1776   $212.18   $212.20   $212.20  
  Purchase #4 $144.28   8.165%   $156.0605   $156.06   $156.05   $156.10  
  Purchase #5 $75.49   7.148%   $80.886   $80.89   $80.90   $80.90  
  Purchase #6 $65.30   10.337%   $72.0501   $72.05   $72.05   $72.10  
  Purchase #7 $229.66   8.846%   $249.9757   $249.98   $250.00   $250.00  
  7 purchase totals = $981.53       $1,056.1578   $1,056.17   $1,056.20   $1,056.30