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 $94.72   11.493%   $105.6062   $105.61   $105.60   $105.60  
  Purchase #2 $99.81   8.873%   $108.6661   $108.67   $108.65   $108.70  
  Purchase #3 $44.30   3.112%   $45.6786   $45.68   $45.70   $45.70  
  Purchase #4 $69.28   7.701%   $74.6153   $74.62   $74.60   $74.60  
  Purchase #5 $168.86   3.203%   $174.2686   $174.27   $174.25   $174.30  
  Purchase #6 $231.85   4.297%   $241.8126   $241.81   $241.80   $241.80  
  Purchase #7 $25.92   10.849%   $28.7321   $28.73   $28.75   $28.70  
  7 purchase totals = $734.74       $779.3795   $779.39   $779.35   $779.40