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 $58.74   11.856%   $65.7042   $65.70   $65.70   $65.70  
  Purchase #2 $104.97   3.589%   $108.7374   $108.74   $108.75   $108.70  
  Purchase #3 $228.48   5.144%   $240.233   $240.23   $240.25   $240.20  
  Purchase #4 $54.85   12.736%   $61.8357   $61.84   $61.85   $61.80  
  Purchase #5 $88.91   9.573%   $97.4214   $97.42   $97.40   $97.40  
  Purchase #6 $232.55   5.526%   $245.4007   $245.40   $245.40   $245.40  
  Purchase #7 $198.61   4.245%   $207.041   $207.04   $207.05   $207.00  
  7 purchase totals = $967.11       $1,026.3734   $1,026.37   $1,026.40   $1,026.20