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 $198.84   5.483%   $209.7424   $209.74   $209.75   $209.70  
  Purchase #2 $215.43   9.374%   $235.6244   $235.62   $235.60   $235.60  
  Purchase #3 $60.35   11.338%   $67.1925   $67.19   $67.20   $67.20  
  Purchase #4 $245.40   9.541%   $268.8136   $268.81   $268.80   $268.80  
  Purchase #5 $139.54   5.670%   $147.4519   $147.45   $147.45   $147.50  
  Purchase #6 $96.55   4.129%   $100.5365   $100.54   $100.55   $100.50  
  Purchase #7 $12.75   3.835%   $13.239   $13.24   $13.25   $13.20  
  7 purchase totals = $968.86       $1,042.6003   $1,042.59   $1,042.60   $1,042.50