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 $211.36   11.497%   $235.6601   $235.66   $235.65   $235.70  
  Purchase #2 $153.93   6.283%   $163.6014   $163.60   $163.60   $163.60  
  Purchase #3 $20.69   11.430%   $23.0549   $23.05   $23.05   $23.10  
  Purchase #4 $96.35   13.700%   $109.55   $109.55   $109.55   $109.60  
  Purchase #5 $225.57   6.843%   $241.0058   $241.01   $241.00   $241.00  
  Purchase #6 $193.29   6.183%   $205.2411   $205.24   $205.25   $205.20  
  Purchase #7 $25.65   3.360%   $26.5118   $26.51   $26.50   $26.50  
  7 purchase totals = $926.84       $1,004.6251   $1,004.62   $1,004.60   $1,004.70