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 $176.84   6.314%   $188.0057   $188.01   $188.00   $188.00  
  Purchase #2 $240.31   9.306%   $262.6732   $262.67   $262.65   $262.70  
  Purchase #3 $175.97   13.644%   $199.9793   $199.98   $200.00   $200.00  
  Purchase #4 $222.56   5.759%   $235.3772   $235.38   $235.40   $235.40  
  Purchase #5 $29.80   12.828%   $33.6227   $33.62   $33.60   $33.60  
  Purchase #6 $106.87   5.281%   $112.5138   $112.51   $112.50   $112.50  
  Purchase #7 $40.98   6.596%   $43.683   $43.68   $43.70   $43.70  
  7 purchase totals = $993.33       $1,075.8549   $1,075.85   $1,075.85   $1,075.90