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 $204.39   11.456%   $227.8049   $227.80   $227.80   $227.80  
  Purchase #2 $33.37   8.608%   $36.2425   $36.24   $36.25   $36.20  
  Purchase #3 $43.57   4.243%   $45.4187   $45.42   $45.40   $45.40  
  Purchase #4 $142.73   6.453%   $151.9404   $151.94   $151.95   $151.90  
  Purchase #5 $221.74   10.691%   $245.4462   $245.45   $245.45   $245.40  
  Purchase #6 $100.56   12.476%   $113.1059   $113.11   $113.10   $113.10  
  Purchase #7 $207.55   3.412%   $214.6316   $214.63   $214.65   $214.60  
  7 purchase totals = $953.91       $1,034.5902   $1,034.59   $1,034.60   $1,034.40