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 $203.41   5.246%   $214.0809   $214.08   $214.10   $214.10  
  Purchase #2 $26.97   7.749%   $29.0599   $29.06   $29.05   $29.10  
  Purchase #3 $213.50   7.396%   $229.2905   $229.29   $229.30   $229.30  
  Purchase #4 $82.92   9.594%   $90.8753   $90.88   $90.90   $90.90  
  Purchase #5 $167.41   5.743%   $177.0244   $177.02   $177.00   $177.00  
  Purchase #6 $236.38   7.421%   $253.9218   $253.92   $253.90   $253.90  
  Purchase #7 $67.91   5.846%   $71.88   $71.88   $71.90   $71.90  
  7 purchase totals = $998.50       $1,066.1328   $1,066.13   $1,066.15   $1,066.20