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 $181.60   11.534%   $202.5457   $202.55   $202.55   $202.50  
  Purchase #2 $14.70   13.415%   $16.672   $16.67   $16.65   $16.70  
  Purchase #3 $122.81   7.629%   $132.1792   $132.18   $132.20   $132.20  
  Purchase #4 $85.28   11.427%   $95.0249   $95.02   $95.00   $95.00  
  Purchase #5 $234.92   4.649%   $245.8414   $245.84   $245.85   $245.80  
  Purchase #6 $215.69   3.403%   $223.0299   $223.03   $223.05   $223.00  
  Purchase #7 $149.76   7.176%   $160.5068   $160.51   $160.50   $160.50  
  7 purchase totals = $1,004.76       $1,075.7999   $1,075.80   $1,075.80   $1,075.70