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 $109.52   8.667%   $119.0121   $119.01   $119.00   $119.00  
  Purchase #2 $193.51   13.599%   $219.8254   $219.83   $219.85   $219.80  
  Purchase #3 $150.77   4.728%   $157.8984   $157.90   $157.90   $157.90  
  Purchase #4 $167.84   8.561%   $182.2088   $182.21   $182.20   $182.20  
  Purchase #5 $95.59   11.155%   $106.2531   $106.25   $106.25   $106.30  
  Purchase #6 $241.77   9.214%   $264.0467   $264.05   $264.05   $264.00  
  Purchase #7 $61.86   3.611%   $64.0938   $64.09   $64.10   $64.10  
  7 purchase totals = $1,020.86       $1,113.3383   $1,113.34   $1,113.35   $1,113.30