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 $232.66   3.803%   $241.5081   $241.51   $241.50   $241.50  
  Purchase #2 $181.37   11.737%   $202.6574   $202.66   $202.65   $202.70  
  Purchase #3 $186.46   9.508%   $204.1886   $204.19   $204.20   $204.20  
  Purchase #4 $24.44   9.208%   $26.6904   $26.69   $26.70   $26.70  
  Purchase #5 $163.90   11.525%   $182.7895   $182.79   $182.80   $182.80  
  Purchase #6 $106.31   8.277%   $115.1093   $115.11   $115.10   $115.10  
  Purchase #7 $96.56   8.536%   $104.8024   $104.80   $104.80   $104.80  
  7 purchase totals = $991.70       $1,077.7457   $1,077.75   $1,077.75   $1,077.80