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 $183.27   12.727%   $206.5948   $206.59   $206.60   $206.60  
  Purchase #2 $222.87   4.124%   $232.0612   $232.06   $232.05   $232.10  
  Purchase #3 $234.59   6.738%   $250.3967   $250.40   $250.40   $250.40  
  Purchase #4 $241.85   5.292%   $254.6487   $254.65   $254.65   $254.60  
  Purchase #5 $57.41   3.799%   $59.591   $59.59   $59.60   $59.60  
  Purchase #6 $134.25   3.214%   $138.5648   $138.56   $138.55   $138.60  
  Purchase #7 $29.96   4.654%   $31.3543   $31.35   $31.35   $31.40  
  7 purchase totals = $1,104.20       $1,173.2115   $1,173.20   $1,173.20   $1,173.30