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 $171.76   13.836%   $195.5247   $195.52   $195.50   $195.50  
  Purchase #2 $247.44   12.278%   $277.8207   $277.82   $277.80   $277.80  
  Purchase #3 $98.47   5.362%   $103.75   $103.75   $103.75   $103.80  
  Purchase #4 $30.93   8.546%   $33.5733   $33.57   $33.55   $33.60  
  Purchase #5 $223.84   3.167%   $230.929   $230.93   $230.95   $230.90  
  Purchase #6 $94.82   7.514%   $101.9448   $101.94   $101.95   $101.90  
  Purchase #7 $154.58   6.761%   $165.0312   $165.03   $165.05   $165.00  
  7 purchase totals = $1,021.84       $1,108.5737   $1,108.56   $1,108.55   $1,108.50