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 $69.95   4.842%   $73.337   $73.34   $73.35   $73.30  
  Purchase #2 $226.58   11.303%   $252.1903   $252.19   $252.20   $252.20  
  Purchase #3 $225.41   4.446%   $235.4317   $235.43   $235.45   $235.40  
  Purchase #4 $91.91   5.282%   $96.7647   $96.76   $96.75   $96.80  
  Purchase #5 $198.54   13.364%   $225.0729   $225.07   $225.05   $225.10  
  Purchase #6 $158.98   8.855%   $173.0577   $173.06   $173.05   $173.10  
  Purchase #7 $231.40   3.280%   $238.9899   $238.99   $239.00   $239.00  
  7 purchase totals = $1,202.77       $1,294.8442   $1,294.84   $1,294.85   $1,294.90