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 $69.34   3.365%   $71.6733   $71.67   $71.65   $71.70  
  Purchase #2 $106.96   7.580%   $115.0676   $115.07   $115.05   $115.10  
  Purchase #3 $201.31   5.146%   $211.6694   $211.67   $211.65   $211.70  
  Purchase #4 $243.27   3.831%   $252.5897   $252.59   $252.60   $252.60  
  Purchase #5 $128.98   3.171%   $133.07   $133.07   $133.05   $133.10  
  Purchase #6 $139.68   7.217%   $149.7607   $149.76   $149.75   $149.80  
  Purchase #7 $20.64   4.145%   $21.4955   $21.50   $21.50   $21.50  
  7 purchase totals = $910.18       $955.3262   $955.33   $955.25   $955.50