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 $90.73   5.162%   $95.4135   $95.41   $95.40   $95.40  
  Purchase #2 $23.73   10.830%   $26.3   $26.30   $26.30   $26.30  
  Purchase #3 $183.28   10.505%   $202.5336   $202.53   $202.55   $202.50  
  Purchase #4 $70.36   5.470%   $74.2087   $74.21   $74.20   $74.20  
  Purchase #5 $172.61   5.391%   $181.9154   $181.92   $181.90   $181.90  
  Purchase #6 $176.56   4.620%   $184.7171   $184.72   $184.70   $184.70  
  Purchase #7 $236.57   12.259%   $265.5711   $265.57   $265.55   $265.60  
  7 purchase totals = $953.84       $1,030.6594   $1,030.66   $1,030.60   $1,030.60