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 $216.94   11.311%   $241.4781   $241.48   $241.50   $241.50  
  Purchase #2 $38.44   7.187%   $41.2027   $41.20   $41.20   $41.20  
  Purchase #3 $73.28   13.564%   $83.2197   $83.22   $83.20   $83.20  
  Purchase #4 $122.64   3.414%   $126.8269   $126.83   $126.85   $126.80  
  Purchase #5 $202.94   3.615%   $210.2763   $210.28   $210.30   $210.30  
  Purchase #6 $219.80   8.565%   $238.6259   $238.63   $238.65   $238.60  
  Purchase #7 $55.59   12.360%   $62.4609   $62.46   $62.45   $62.50  
  7 purchase totals = $929.63       $1,004.0905   $1,004.10   $1,004.15   $1,004.10