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 $194.54   4.661%   $203.6075   $203.61   $203.60   $203.60  
  Purchase #2 $77.27   13.397%   $87.6219   $87.62   $87.60   $87.60  
  Purchase #3 $221.72   3.582%   $229.662   $229.66   $229.65   $229.70  
  Purchase #4 $177.93   13.838%   $202.552   $202.55   $202.55   $202.60  
  Purchase #5 $190.68   7.239%   $204.4833   $204.48   $204.50   $204.50  
  Purchase #6 $31.63   7.718%   $34.0712   $34.07   $34.05   $34.10  
  Purchase #7 $203.53   7.689%   $219.1794   $219.18   $219.20   $219.20  
  7 purchase totals = $1,097.30       $1,181.1773   $1,181.17   $1,181.15   $1,181.30