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 $203.92   5.301%   $214.7298   $214.73   $214.75   $214.70  
  Purchase #2 $187.73   9.874%   $206.2665   $206.27   $206.25   $206.30  
  Purchase #3 $59.43   3.598%   $61.5683   $61.57   $61.55   $61.60  
  Purchase #4 $179.62   12.842%   $202.6868   $202.69   $202.70   $202.70  
  Purchase #5 $167.39   10.594%   $185.1233   $185.12   $185.10   $185.10  
  Purchase #6 $220.45   11.116%   $244.9552   $244.96   $244.95   $245.00  
  Purchase #7 $25.68   9.498%   $28.1191   $28.12   $28.10   $28.10  
  7 purchase totals = $1,044.22       $1,143.4490   $1,143.46   $1,143.40   $1,143.50