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 $228.96   11.247%   $254.7111   $254.71   $254.70   $254.70  
  Purchase #2 $146.45   6.819%   $156.4364   $156.44   $156.45   $156.40  
  Purchase #3 $146.73   7.467%   $157.6863   $157.69   $157.70   $157.70  
  Purchase #4 $95.58   7.391%   $102.6443   $102.64   $102.65   $102.60  
  Purchase #5 $224.75   3.366%   $232.3151   $232.32   $232.30   $232.30  
  Purchase #6 $40.36   3.661%   $41.8376   $41.84   $41.85   $41.80  
  Purchase #7 $96.30   9.334%   $105.2886   $105.29   $105.30   $105.30  
  7 purchase totals = $979.13       $1,050.9194   $1,050.93   $1,050.95   $1,050.80