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 $91.62   5.280%   $96.4575   $96.46   $96.45   $96.50  
  Purchase #2 $124.59   3.550%   $129.0129   $129.01   $129.00   $129.00  
  Purchase #3 $150.36   6.722%   $160.4672   $160.47   $160.45   $160.50  
  Purchase #4 $207.31   9.673%   $227.3631   $227.36   $227.35   $227.40  
  Purchase #5 $54.38   12.617%   $61.2411   $61.24   $61.25   $61.20  
  Purchase #6 $75.29   11.747%   $84.1343   $84.13   $84.15   $84.10  
  Purchase #7 $230.68   6.721%   $246.184   $246.18   $246.20   $246.20  
  7 purchase totals = $934.23       $1,004.8601   $1,004.85   $1,004.85   $1,004.90