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 $57.25   6.818%   $61.1533   $61.15   $61.15   $61.20  
  Purchase #2 $94.50   11.294%   $105.1728   $105.17   $105.15   $105.20  
  Purchase #3 $211.57   12.497%   $238.0099   $238.01   $238.00   $238.00  
  Purchase #4 $159.93   12.128%   $179.3263   $179.33   $179.35   $179.30  
  Purchase #5 $192.61   6.736%   $205.5842   $205.58   $205.60   $205.60  
  Purchase #6 $167.66   12.771%   $189.0719   $189.07   $189.05   $189.10  
  Purchase #7 $103.75   11.516%   $115.6979   $115.70   $115.70   $115.70  
  7 purchase totals = $987.27       $1,094.0163   $1,094.01   $1,094.00   $1,094.10