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 $91.26   5.818%   $96.5695   $96.57   $96.55   $96.60  
  Purchase #2 $166.75   7.387%   $179.0678   $179.07   $179.05   $179.10  
  Purchase #3 $168.64   3.332%   $174.2591   $174.26   $174.25   $174.30  
  Purchase #4 $97.83   8.654%   $106.2962   $106.30   $106.30   $106.30  
  Purchase #5 $19.89   13.700%   $22.6149   $22.61   $22.60   $22.60  
  Purchase #6 $96.42   6.372%   $102.5639   $102.56   $102.55   $102.60  
  Purchase #7 $60.95   10.685%   $67.4625   $67.46   $67.45   $67.50  
  7 purchase totals = $701.74       $748.8339   $748.83   $748.75   $749.00