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 $110.69   11.256%   $123.1493   $123.15   $123.15   $123.10  
  Purchase #2 $192.45   5.452%   $202.9424   $202.94   $202.95   $202.90  
  Purchase #3 $169.73   7.163%   $181.8878   $181.89   $181.90   $181.90  
  Purchase #4 $21.68   6.220%   $23.0285   $23.03   $23.05   $23.00  
  Purchase #5 $30.94   9.137%   $33.767   $33.77   $33.75   $33.80  
  Purchase #6 $220.55   11.384%   $245.6574   $245.66   $245.65   $245.70  
  Purchase #7 $184.86   4.194%   $192.613   $192.61   $192.60   $192.60  
  7 purchase totals = $930.90       $1,003.0454   $1,003.05   $1,003.05   $1,003.00