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 $85.83   9.701%   $94.1564   $94.16   $94.15   $94.20  
  Purchase #2 $31.53   9.249%   $34.4462   $34.45   $34.45   $34.40  
  Purchase #3 $19.81   3.203%   $20.4445   $20.44   $20.45   $20.40  
  Purchase #4 $233.75   6.333%   $248.5534   $248.55   $248.55   $248.60  
  Purchase #5 $243.93   4.400%   $254.6629   $254.66   $254.65   $254.70  
  Purchase #6 $184.68   4.228%   $192.4883   $192.49   $192.50   $192.50  
  Purchase #7 $142.82   7.342%   $153.3058   $153.31   $153.30   $153.30  
  7 purchase totals = $942.35       $998.0575   $998.06   $998.05   $998.10